The ingestion of hot food and beverages has repeatedly been postulated as a risk factor for cancer of the esophagus. Although several studies have been performed on the correlation of the consumption of hot tea and esophageal cancer, no research has heretofore documented, by actually measuring, the temperature at which the tea is consumed. Therefore, a tea temperature measurement study was carried out in the Caspian Littoral of Iran, where the frequency of esophageal cancer is the highest in the world. The study was conducted during a population-food-habits survey in 1968 to 1969, which was performed before statistics were available regarding the incidence rate or geographic distribution of this disease in the region. Ten years later, when the results of the Caspian Cancer Registry were analyzed, the data from this nutritional study was compared with the regional distribution of esophageal cancer. A geographic correlation exists between the frequency of consumption of hot tea and the incidence of esophageal cancer. Seventy-two percent of the people in the low-risk region of esophageal cancer drank their tea at the relatively moderate temperature of below 55 degrees C, compared with only 3% in the high risk region. More importantly, 62% of the adult population in the high-risk region, as opposed to 19% in the low-risk region, drank their tea at a temperature of over 65 degrees C. In addition to the thermal irritation of hot tea, the following considerations cannot be ignored: the carcinogenicity role of tannins; the cancer-promoting effect of phenols; and the absorption facilitating role of hot tea. Alcohol and tobacco, the most important risk factors for cancer of the esophagus in many countries, play a negligible role in the cause of this disease in northern Iran. In this region, nutritional deficiencies--a special diet for pregnant women composed of sour pomegranite seeds, black pepper, and garlic; consumption of bread contaminated with silica fibre; and ingestion of opium and opium dross--combined with long-lasting and daily thermal irritation of the esophagus with very hot tea play an important role in the development of this disease. The inhabitants of the high-risk area consumed roughly 2.5 times more tea than their counterparts in the low-risk area. In addition, the mean daily consumption of tea leaves per person (average) was 5.7 g and 3.8 g, respectively.