Cisplatin and melphalan given ip exert a synergistic therapeutic effect against ascitic P388 leukemia in mice and have different dose-limiting toxic effects as well as favorable pharmacokinetic characteristics in ip phase I studies. We gave a total of 98 courses of cisplatin (escalated from 40 to 120 mg/m2) and melphalan (escalated from 12 to 30 mg/m2) to 30 patients with ip tumors, most of whom had residual ovarian cancer following iv cisplatin-containing regimens. Treatment was delivered in 2 L of 0.9% NaCl through a Tenckhoff catheter with or without a Port-a-Cath system every 28 days for one to nine cycles. Myelosuppression was dose-related and leukopenia was dose-limiting. The maximum tolerated dose was 120 mg of cisplatin/m2 and 20 mg of melphalan/m2. With the exception of treatment-induced nausea and vomiting, nonhematologic toxic effects were mild and no (or very little) local toxicity occurred. Pharmacokinetic analyses showed that the areas under the peritoneal concentration versus time curve averaged 16-fold and 17-fold more than the area under the plasma curve for cisplatin and melphalan, respectively. Objective responses were documented by third-look laparotomy in ovarian cancer patients with minimal (less than 2 cm) residual disease.