Six patients were administered cisplatinum (CDDP) i.p. There were four cases with peritoneal dissemination of gastric cancer after gastrectomy and the other two, for whom prophylactic intraperitoneal administration of CDDP had been attempted to prevent peritoneal metastasis. The dose of CDDP was 75-140 mg/body (58-90 mg/m2). The results were 1 PR, 2 NC and 1 PD. The PR case was given intraperitoneal CDDP combined with RF thermotherapy. Liver dysfunctions, renal dysfunctions, bone marrow suppressions, and GI tract disturbances were observed as toxic reactions. The degrees of side effects after i.p. administration were less severe than after i.v. administration. However the indication of CDDP i.p. administration should be decided after case conferences. On pharmacokinetics, non-protein bound platinum was detected at 24 hours after i.p. administration, in ascites and plasma. The concentration of platinum in ascites was about three-fold than in plasma. It was considered that CDDP absorption from ascites into plasma depended on the state of peritoneal dissemination of cancer.