A quasi-historical cohort study method was used to collect the data of male stomach and liver cancer death from 1984 to 1988 in male residents (> or = 30 years old) of three tap-water-drinking communities at the upper, middle and lower reaches of the Huangpu River. Total person-years observed are 184,645. The result shows that the world standard population standardized cut-off mortalities (> or = 30 years old) of male stomach and liver cancer increase gradually from the upper to lower reaches. The mortalities from the upper to the lower reaches are 62.7, 86.2 and 146.0/100,000 person-years for male stomach cancer and 56.9, 67.7 and 81.3/100,000 person-years for male liver cancer, respectively. This trend is consistent with the change of the rate of positive Ames Test results of drinking water from the upper to lower reaches (0, 70, 100%). It suggests that a causal correlation may exist between the two. The distribution of other possible risk factors in the three communities is also described.