This report describes the effect of intraperitoneal administration of CDDP for the treatment of peritoneal dissemination (P) in 20 patients with gastric cancer. Eight patients after palliative resection, 4 after non-resection and 8 with recurrent cancer were given 25 mg of CDDP through a reservoir (Infuse-A-Port) implanted in the abdominal wall once a week. Simultaneously, 400 mg/body/day of UFT and 2 mg/body/week of Lentinan were administered. Twelve of the patients died of disease at 6-19 months (median 7 months), but 8 have survived 3 to 15 months (median 6 months). Complete and partial responses were obtained in 7 of the 8 patients with recurrence (88%) for malignant ascites. No patient showed any toxicity from treatment. All patients receive the treatment in the outpatient clinic after discharge, and 17 patients have shown a long hospital-free survival.