The pharmacokinetic studies of intraperitoneal cisplatin (CDDP) for gastric cancer were discussed elsewhere, but those studies were investigated in patients with ascites. The purpose of this study is to compare the difference in pharmacokinetics between patients with malignant ascites and those curatively resected without ascites. One hundred mg of CDDP and 300 ml of saline were administered intraperitoneally for 9 curatively resected patients by catheter just after operation, and the same doses of CDDP were administered for 3 advanced or recurrent patients with ascites just after removal of whole fluid. Blood samples were corrected at 6 points after administration. Results were as follows: The 0-t area under the curve (AUC) and the Cmax of both total and free CDDP in the patients without ascites was higher than in the patients with ascites. The 0-infinity AUC and MRT of the ascites patients were higher than in the patients without ascites. These data suggest that intraperitoneal CDDP chemotherapy for gastric cancer as an adjuvant setting is more effective than chemotherapy for advanced malignant ascites patients.