We have conducted a clinical trial to evaluate the effectiveness of continuous hyperthermic peritoneal perfusion with mitomycin C (CHPP-M) as prophylactic treatment of peritoneal recurrence of gastric cancer. Between January 1983 and October 1985, 82 patients with macroscopic serosal invasion but no macroscopic peritoneal metastasis undergoing potentially curative resection of gastric cancer, were divided into two groups by random sampling: 42 patients were scheduled to receive CHPP-M, while 40 would not receive such treatment. The CHPP-M was administered immediately after closure of the abdomen following gastric resection, while the patient was still on the operating table under general anesthesia. The 5-year survival rate (71.5% of the patients in the CHPP-M group was higher than that (59.7%) of those in the control group. Although postoperative follow-up periods are not long enough, the longer survival obtained in the patients treated with CHPP-M should be emphasized, since no effective means of preventing peritoneal recurrence of gastric cancer is so far available.