Serum gastrin levels were measured by radioimmunoassay in 62 patients with colorectal neoplasms (40 with adenomatous polyps and 22 with cancer) and 40 controls. Fasting serum gastrin in both the polyp (73.93 +/- 6.5 pg/ml) and the cancer (99 +/- 19.7 pg/ml) groups was significantly higher than those of the control group (42.65 +/- 2.2 pg/ml). These findings suggest that hypergastrinemia may be an etiologic factor in colorectal neoplasia.