Twenty-six adult patients were entered in a phase I trial of carboplatin, a new cisplatin derivative with reduced potential for nephrotoxicity. All patients had solid tumors and the median World Health Organization performance score was 2 (0-3). Twelve patients had not received prior chemotherapy. The drug was administered as a 15-minute IV infusion, without pre- or posthydration, at daily doses of 40-125 mg/m2 for five consecutive days. Antiemetics were given only if needed. Thrombocytopenia and neutropenia were dose related and dose limiting. One patient died from septic shock at the highest dose level. Nonhemolytic anemia was also encountered. Nausea and vomiting were experienced by most patients but gastrointestinal intolerance was severe in only two patients. One patient had hypercreatininemia, which was minor and rapidly reversible. Other toxic effects consisted of negligible fatigue, paresthesia, pruritus, local pain, stomatitis, headache, and alopecia. Although none of the patients achieved a partial or complete response, antitumor effect was strongly suggested in two patients with thyroid and cervix cancer, respectively. Carboplatin is an attractive candidate for phase II trials. In good-risk patients, such trials could be initiated at a daily dose of 100 mg/m2 for five consecutive days every five to six weeks.