We studied the effect of early postoperative chemotherapy, including 5-fluorouracil (5-FU) for 5 days for patients with gastric cancer following noncurative resection. The study was prospectively randomised and controlled, and 162 (87.1%) of 186 were eligible candidates for statistical assessment. Patients randomised to group A received therapy that is used widely to treat patients with gastric cancer in Japan; mitomycin C (MMC), OK-432, UFT and PSK. Patients randomised to group B received the same drugs given to group A plus 5-FU bolus injections for 5 days, beginning on postoperative day 2. There were no differences in prognostic factors and doses of the drugs prescribed, except for 5-FU. There was no difference in the toxicity rate between the groups. Generalised Wilcoxon test revealed a P value of 0.169, and the 50% survival rate improved 1.4-fold in patients with gastric cancer treated with early postoperative chemotherapy of MMC, OK-432 plus 5-FU injection.