We performed a phase I-II trial of escalating doses of cisplatin (CDDP: 50-100 mg/m2 per course) plus carboplatin (CBDCA: 300-400 mg/m2 per course) as a potential way in which to maximize platinum doses without causing excessive toxic effects in patients with advanced ovarian cancer. Thirty-three patients with nonoptimally debulked disease of FIGO (International Federation of Gynecology and Obstetrics) stages IIc-IV [median age: 60 yr; median WHO (World Health Organization) performance status: 2; no prior chemotherapy] received a median of six courses of therapy. CBDCA was infused on day 1 and CDDP on day 2 with an aggressive 48-hour hydration regimen. Myelosuppression was dose-limiting: at the highest dose levels, WHO grade 4 neutropenia and thrombocytopenia led to dose reduction and/or treatment delay in 45% of the patients. Nonhematologic toxic effects included acute nausea and vomiting (97% of the patients), mild alopecia (45%), ototoxic effects (39%), neurotoxic effects (21%), and renal toxic effects (serum creatinine greater than 1.5 mg/dL: 12.5%). The pathologic complete response rate was 22%. We conclude that CBDCA and CDDP can be given safely in combination at reasonably high doses (CBDCA at 300 mg/m2 per course and CDDP at 100 mg/m2 per course) over a 6-month period, provided a close hematologic follow-up is conducted. Randomized clinical trials are needed to define whether this regimen is any better than standard combination chemotherapy.