A phase II study of the effectiveness and toxicity of carboplatin in the treatment of metastatic or locally advanced endometrial cancer was carried out by the Southwest Oncology Group. Thirty-two patients were registered in the study and 23 were fully evaluable for response and toxicity. Carboplatin was administered in a dose of 400 mg/m2 at 28-day intervals without concomitant hydration if blood counts had recovered sufficiently. There were seven responses (two complete and five partial responses) among the 23 evaluable patients, for an overall response rate of 30%. Four (two of two complete responders and two of five partial responders) of the seven responding patients remain alive at 839+ to 987+ days from the start of therapy. The two complete responders and one of the partial responders had small-volume disease, which may have contributed to their prolonged survival. Myelosuppression was the most prominent toxicity encountered. Seventeen of 27 patients evaluable for toxicity developed platelet counts of less than 75 X 10(3)/muL during therapy, but no hemorrhagic complications were encountered. Leukopenia was less prominent, with only nine of 27 patients developing white blood cell counts of less than 3.0 X 10(3)/microL. No important nephrotoxicity or neurotoxicity was observed. Emesis occurred in ten of 27 patients but was not dose-limiting. No unexpected toxicities were encountered. Carboplatin appears to be an active agent in the treatment of endometrial carcinoma.