After en bloc resection of gastric adenocarcinoma, 180 patients were randomized to 2 years of 5-fluorouracil (5-FU) + semustine (MeCCNU) chemotherapy or to observation only. After a median follow-up time of 64 months, 48 of 89 control patients and 51/91 treated patients recurred (P less than 0.71). The sites of recurrent cancer were similar for both groups: liver, 32%; local esophagus or stomach, 51%; abdominal nodes and peritoneum, 38%; and extra-abdominal nodes, 14%. The survival curves overlap; 51/89 controls and 57/91 treated patients died with a median survival of 32.7 and 36.6 months, respectively (P less than 0.73). Treated patients experienced clinically important hematologic toxicity and two treated patients died of marrow failure with leukemia. Because of the toxicity and the lack of effectiveness, adjuvant 5-FU + MeCCNU is not recommended for patients with resectable gastric cancer.