Carboplatin (CBDCA) is an active agent in the treatment of acute leukemia and is associated with limited extramedullary toxicity. Simultaneous phase II trials were conducted by the Southwest Oncology Group in adult patients with relapsed or refractory acute myeloid leukemia (AML). CBDCA was given as a continuous infusion at a dose of 300 mg/m2 daily for 5 days. Three (8%) of the 37 eligible patients in the relapsed group achieved complete remissions (CRs) lasting 3, 4, and 26 months. Entry of patients was stopped early in the refractory group due to slow accrual and in the relapsed group due to low CR rate. For both groups combined, the CR rate was 3/45 or 7% (95% confidence interval 3-18%). There were 12 fatal toxicities. Four patients died of intracerebral hemorrhage, three of infection, and five of hepatic and/or renal failure. Nonhematologic grade 4 toxicity included diarrhea in three patients, hyperbilirubinemia in four, and mucositis and renal toxicity in one each. These results suggest that CBDCA should not be considered for treatment of relapsed or refractory AML patients with prior high-dose therapy.