A phase II clinical trial of carboplatin infusion in high-risk acute nonlymphoblastic leukemia. Carboplatin (CBDCA) is a second-generation platinum drug that has been shown to be useful when used as a continuous infusion in treatment of refractory adult leukemia. We report on the effectiveness of continuous infusion CBDCA, 300 mg/m2/d x 5 days, as evaluated in nine patients with secondary acute nonlymphocytic leukemia (ANLL) (seven previous myelodysplastic syndrome and two treatment-associated ANLL), three ANLL patients in first relapse, six refractory ANLL, and nine patients with blastic phase of chronic myelogenous leukemia (BP-CML). All patients were considered assessable. The response rate was 44% (eight complete remissions [CRs], four partial remissions [PRs]). Median duration of postchemotherapy neutropenia was 36 days (range, 18 to 45). Therapy was well tolerated, and toxicity was mainly hematologic and nondose-limiting. Despite prolonged neutropenia, severe infections were rarely seen, and most patients were managed as outpatients. Twelve patients had nausea and vomiting, two had symptomatic hypomagnesemia, and one patient showed reversible ototoxicity. Because of substantial antileukemic activity and unusual extrahematologic toxicity, CBDCA appears to be an effective second-line agent in the treatment of ANLL and should be considered for upgrading to first-line treatment regimens. 