Our objective was to determine whether chronic hypergastrinemia enhances chemical induction of rat colorectal cancers. Forty-five rats were randomized to sham operation or antral exclusion. Following a 2-week postoperative recovery period all rats were treated with 1,2-dimethylhydrazine (10 mg/kg) intraperitoneally for 20 weekly doses. Seven weeks later, the rats were killed. Blood was assayed for gastrin by radioimmunoassay. Tumor number, location, size, weight and histology were determined. The 23 rats receiving antral exclusion were hypergastrinemic compared with the 22 sham operated rats. All hypergastrinemic rats developed tumors while only 72.7% of normogastrinemic rats developed tumors. Hypergastrinemia increased the number of tumors/rat, total tumor weight/rat and total tumor volume/rat.