Epidemiologic studies were undertaken on the Caspian littoral of Iran to investigate the geographic distribution of factors that might underlie the signal differences in incidence of cancer of the esophagus. In zones of contrasting incidence and sex ratio, information was obtained on food intake, smoking and drinking patterns (including tea), other personal habits, occupation, economic and agricultural practices, and methods of food storage preservation, and preparation. The diet in the highest incidence area was markedly restricted to bread and tea. The poor quality of the diet itself was thought to have a role in the increased risk of developing esophageal cancer. The use of opium and sesame oil, consumption of sheep's milk and yogurt, the chewing of nass (confined to men), and the use of dyes (confined to women) were also more prevalent in the high incidence areas. Typical dietary items were analyzed for the polycyclic aromatic hydrocarbons, volatile nitrosamines, aflatoxins, nitrates, and nitrites. The results showed no unusual levels of any of the carcinogens tested or geographic differences.