There are 1,000 new cases of zombiism reported in Haiti each year. Are zombies really the dead brought back to life by sorcerers, as locals believe, or are they people suffering from mental illness? Roland Littlewood went to Haiti to find out

Probably no local phenomenon is as infamous as the Haitian zombie. The concept of the "walking dead" - soulless corpses said to have been revived by witchcraft - was implanted in western minds following the 1915 occupation of Haiti by the United States. The Harlem poet Zora Neale Hurston wrote an enthusiastic travel piece from the West Indian republic and since then zombies have featured in countless movies: I Walked with a Zombie, The Night of the Living Dead, even, at its most absurd, Chopperchicks in Zombietown.

Most people dismiss the idea of "walking dead" as exotically improbable, yet Haitian doctors regard zombification as the consequence of deliberate poisoning, while local clergy explain it as sorcery. Zombies are often recognised in Haitian villages - by staring expressions, nasal intonation, purposeless actions and limited speech - sometimes reappearing years after their registered death. Estimates suggest 1,000 new cases a year.

Turning someone into a zombie is treated as murder under the Haitian Penal Code. Haitians believe that, either by poisoning or by sorcery, a young person suddenly becomes ill, is recognised as dead and placed in a tomb, only to be stolen by a boko (sorcerer), and secretly returned to life - though not to full awareness. Rather than being buried, Haitians are interred in above-ground tombs, (easily broken open), next to family homes. Haitian schemata of body, mind and spirit recognise a separation of the corpse, the cadavre (physical body) with its gwo-bon anj (animating principle) from the ti-bon anj (awareness and memory). According to local beliefs the ti-bon anj is retained by the sorcerer, usually in a bottle: he either extracts it through sorcery, which leaves the victim apparently dead, or captures it after a natural death before it strays far from the body. The animated body remains without will and becomes the sorcerer's slave, induced to remain a slave through chaining and beating or more poisoning. This is the "zombie" popularised by western cinema.

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There are different explanations for how a zombie might escape a sorcerer's clutches and return to its family. The bottle holding the zombie's spirit might break, the sorcerer might inadvertently feed the zombie salt, or the zombie might be released through divine intervention. Few doctors claim to be able to return a zombie to its original health - the matter is reserved for Le Grand Maitre (the remote God recognised by voodoo practitioners).

I interviewed zombies and sorcerers in Haiti to try to ascertain whether zombies really are the supposed deceased individuals their relatives claim to have recognised. Using brain scans and DNA tests I was open to the possibility of discovering a clinical pattern that might suggest mental illness as a cause of the zombie condition.

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Wilfred D, 26, is the eldest son of an alleged former tonton macoute, one of Haiti's feared secret police. His father, my principal informant, was the only senior family member who had attended elementary school. Wilfred was intelligent, and a cousin had promised to pay for a college education if he did well at secondary-school. But when he was 18 he fell ill: "his eyes turned yellow", he "smelled bad like death" and "his body swelled up". Suspecting sorcery, his father asked his elder brother to seek advice from a sorcerer, but Wilfred died three days later and was interred in a tomb near a female cousin's house.

Nineteen months later "Wilfred" reappeared, was able to recognise his father and accused his uncle of having zombified him. He was recognised as a zombie by other villagers, the local Catholic priest and magistrate, and has since remained in his father's house, his legs secured to a log to prevent him wandering. At the father's request, the uncle was arrested and sentenced to life imprisonment for zombification. He confessed that he was jealous of his brother, who had used his literacy to register the family land in his own name. According to his friend, who first identified him when he reappeared, Wilfred mentioned stealing two coconuts from his uncle who, finding him drinking them, seized them to use for sorcery. Another friend said the uncle rubbed a poison on Wilfred's arm.

Having escaped from prison during the political turmoil of 1991, the uncle was traced. Agreeing to an interview in exchange for protection, he denied sorcery or poisoning, saying the case was a trick by Wilfred's father to expropriate his land, and his own confession was induced through torture by local police.

I interviewed Wilfred, a slight, scowling man who looked much thinner and younger than in an old photograph his parents held. He had limited mobility, spending his time alone in a characteristic position, lower limbs to the left, upper limbs to the right, rarely speaking spontaneously and then only in single words. He could not describe his period of burial or enslavement but agreed he was malad (ill) and zombi. His parents said he was not incontinent but they had to bathe him. He had no interest in anything. Wilfred's eyes continually scanned about with no clear intent, his hands picking aimlessly at his nails. His wrists were scarred, consistent with abrasions caused by chains or wire. He experienced periods of anger when he would hit out, generally after being teased, and fits during sleep.

Wilfred was agitated during his CT scanning (which, of course, recalled a tomb). On visiting his tomb, he showed no emotion but lent blankly against it, becoming irritated when teased about his death by neighbours. His CT scan was normal. My diagnosis was organic brain syndrome and epilepsy.

My second case was that of Marie M. Before her death, Marie was the younger sister of Michel M, who described her as formerly a friendly but shy girl, who, like him, had never attended school. The family was poor, living in a two-room public housing project in Les Cayes. Some 20 years ago Marie joined friends in prayers for a neighbour who had been zombified. She herself then fell ill, her body swelled up and she died a few days later. The family suspected revenge sorcery.

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After 13 years, "Marie" reappeared in the market of Les Cayes, with an account of having been kept as a zombie in a village 100 miles away and having borne a child to another zombie or perhaps to the sorcerer. On the death of the sorcerer, she said, she was released and travelled home on foot. On his sister's return, Michel recognised her as a zombie and started a daily healing service.

Marie looked much younger than her age, with a small head and ears, thin and slight. She responded to attention, asked questions spontaneously, giggled frequently and laughed inappropriately. Her ready acquiescence to any requests made me worry about her vulnerability away from her family; when unattended she would often wander away. Marie could make simple requests for food and gifts, and agreed she was ill but not that she was a zombie. Her brother said she was duller than she had been but she had never been very clever. Her self-care was normal but her family said she enjoyed being cuddled. Her CT scan was within normal limits. My presumptive diagnosis was learning disability.

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With Marie's agreement I took her to Cabaret, where she said she had been kept as a zombie, only to have her recognised immediately as a "simple" local woman, enticed away nine months before by a band of musicians. By now two families were insisting that Marie was theirs, accusing each other of zombification. Both gave evidence to the local police. Marie's Cabaret "daughter" and "brother" then appeared. They resembled her in appearance, mannerisms and minor learning disability. Marie recognised the daughter, whom she had previously named correctly to us, but insisted that the daughter's father was a fellow zombie. Marie had apparently been abducted (or wandered away) from Cabaret and ended up at Les Cayes, where Michel recognised her as his deceased and now zombified sister.

We conducted biomedical tests on both supposed zombies. DNA fingerprinting suggested Wilfred was not the son of his putative parents; while Marie was related neither to Michel, nor to her brother in Cabaret, although she probably was the mother of her Cabaret daughter. I came to the conclusion that although it is unlikely that there is a single explanation for all cases where zombies are recognised by locals in Haiti, the mistaken identification of a wandering mentally ill stranger by bereaved relatives is the most likely explanation in many cases. People with a chronic schizophrenic illness, brain damage or learning disability are not uncommon in rural Haiti, and they would be particularly likely to be identified as zombies.

But I cannot exclude the possibility that, given that death is locally recognised without medical certification and burial occurs within a day of death, a person might be entombed alive. There has already been medical interest in the possibility that zombification may be an empirical state - catalepsy or motor paralysis - induced by neurotoxins followed by the retrieval and revival of the "dead" person in the tomb. Among the poisons implicated are tetrodotoxin (from the puffer fish) with datura stramonium used to "revive" and control the zombie. The use of datura to revive entombed people and its repeated administration during the period of zombie slavery could produce a state of extreme passivity.

That sorcerers enslave zombies on secret agricultural grounds is implausible given the population density of Haiti. Yet, in the political terror and social instability during and after the Duvalier regime, numerous cases of abduction, torture and sexual slavery cloaked in voodoo have maintained an uncertain status. Beyond biomedical analysis, a more nuanced consideration of zombification requires sociological research that might explore how the zombie recalls Haiti's national history as "the black republic" of former slaves who have continued to face the ever-present threats of political dependency, racism and loss of self-determination.

Roland Littlewood is professor of anthropology and psychiatry, University of London.

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Like most sorcerers, Altesse Paul is also a priest with his own temple as well as convenor of one of the secret societies that have been implicated in zombification and are illegal under the Haitian Penal Code. He thought the cases of Marie and Wilfred were plausible, and he recognised as part of his own pharmacopoeia both a puffer fish and a branch of Hippomane mancinella ("zombie apple"), commonly cited as the astringent used by sorcerers in topical application of a poison. He showed me bottles that contained captured zombie spirits, but he said that he had sold all his physical zombies to local cultivators and other sorcerers; contact with them would be dangerous for us.

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