<正> It is well known that there are huge geographic variations in cancer rates in mainland China. For example, The National Cancer Control Office of the Ministry of Public Health (1979) reported that in the 1970s, cancer mortality rates for most cancers were found to be more than 20-fold greater in some counties in others (Table 1). Esophageal cancer rates for males are a few hundred fold greater in the highest county when compared with the lowest county. The mortality rate for all cancers combined for males is 21 fold greater in the county with the highest mortality than in the county with the lowest rate. According to Doll and Peto (1981), about one third of human cancer death is avoidable by appropriate modification of the diet. Therefore, diet is very likely to have an important part in causing these huge geographic variations. The possible role of various mutagens and carcinogens (e.g. aflatoxin, N-nitroso compounds) in locally produced and consumed foods has been strongly suggested and widely acknowle