The effectiveness of Bestatin on the prognosis of gastric cancer patients was investigated in a randomized controlled trial of postoperative adjuvant chemotherapy. One hundred and sixty-two cases of gastrectomized patients were divided into two groups; a Bestatin group (83 cases, 1/2MF'C [mitomycin C 2 mg and cytosine arabinoside 20 mg i.v. twice a week for 3 weeks, FT-207 400 mg/day i.v. for 3 weeks] followed by Bestatin 30 mg/day and FT-207 0.6 g/day p.o.) and a control group (79 cases, 1/2MF'C followed by FT-207 alone). No significant differences in background factors between the two groups were found. Bestatin was slightly effective in improving the three-year survival rates of gastric cancer patients, but this was not significant. However, survival rates in the Bestatin group in Stage II, curatively operated cases, and n (-) ps (+) cases were significantly higher than those of the control group during the same postoperative period. Bestatin prolonged the disease-free interval in curatively resected cases. Thus, efficacy of Bestatin in improving survival rates was observed in the early stages of disease, but it is suggested that combination a stronger chemotherapeutic regimen may be effective in advanced cases.