Iproplatin was administered intravenously over 30 min daily for 5 consecutive days every 3 weeks to 80 evaluable patients with a variety of refractory solid tumor malignancies. Thrombocytopenia was the dose-limiting toxicity. Reversible drug-induced renal dysfunction was observed in 3 patients. One patient sustained mild ototoxicity but neurotoxicity was not encountered. Transient neutropenia, anemia, nausea, vomiting, diarrhea, elevations of liver enzymes, alopecia, and skin rash also occurred. The spectrum and severity of toxicity of iproplatin were found to differ from those of cisplatin. The maximally tolerated dose (MTD) was 45 mg/m2/day in patients who received prior chemotherapy and 65 mg/m2/day in those who did not. No complete responses occurred. Partial responses were obtained in 2/15 patients with colon cancer, 3/18 with breast cancer, 2/4 with carcinoma of unknown primary site and 1/2 with pancreatic cancer. Thirteen patients with lung (5), breast (4), colon (2), head and neck (1) and cervical (1) cancers had stable disease. Based on the different toxicity profiles between iproplatin and cisplatin and the possible antitumor efficacy of the former, phase II investigation of iproplatin has been initiated.