A group of 5908 men provided serum samples during their study examination from 1967 to 1970. After a surveillance period of over 20 years, 121 incident cases of tissue-confirmed gastric cancer were identified. Their stored sera and those of 121 matched controls from the study population were tested for serum ferritin and transferrin levels. Because of the suggested effects of previous thawing on the serum results, detailed data analyses were limited to the 46 cases and matched controls whose sera were never thawed before this study. The mean serum levels (In ng/ml) were 5.26 for the 46 gastric cancer cases and 5.68 for their controls (P < 0.01). For serum transferrin, the mean levels (mg/dl) were 249.8 for cases and 254.1 for controls (P = 0.53). The inverse association with serum ferritin, which reflect total iron body stores, was stronger for the 21 cases diagnosed within 15 years of examination (P = 0.02) than for the 25 cases diagnosed after 15 years (P = 0.15). The limitations of the study and the implications of its findings are discussed.