In order to evaluate the utility of combination chemotherapy with intra-peritoneal infusion of CDDP and continuous intravenous infusion of 5-FU, we performed this therapy in 23 primary gastric cancer patients with peritoneal metastasis. CDDP was administered intraperitoneally at a dose of 70 mg/m2 over 2 hours on day 1, and 5-FU was continuously administered intravenously at a dose of 700 mg/m2 for 5 consecutive days from day 1, respectively. This treatment was given twice. Median survival time with this treatment was 343 days, and the depth of invasion was selected as an independent prognostic factor according to multivariate analysis. Five patients (21.7%) have survived more than 3 years. Major toxicities were less than Grade 2 except for two patients with each anemia (Grade 3) and venous thrombosis (Grade 3), respectively. This regimen appears to be feasible and effective for gastric cancer patients with peritoneal metastases. Long term survival may be obtained in patients without adjacent organ invasion.