Carboplatin (CBDCA) is a second-generation platinum analog with prominent myelotoxicity and modest extramedullary toxicity. We performed a phase I study of CBDCA in adult patients with relapsed acute leukemia. Therapy was administered as a five-day continuous infusion. The initial dose of 875 mg/m2 over five days was escalated in 15% increments to a final dose of 2,100 mg/m2 over five days. Twenty-eight patients received 35 induction courses of CBDCA, including two patients who achieved a complete remission (CR) following the first course, and received a second induction course at the time of relapse. Therapy was well tolerated. No grade 3 or 4 extramedullary toxicity was seen. Myelosuppression was regularly observed, with prolonged myelosuppression at 2,100 mg/m2 over five days being the indication to cease dose escalation. Eight of 28 patients (28.5%) responded to CBDCA therapy (six CR, two partial remission [PR]) or ten of 30 initial induction courses (33.3%). Continuous-infusion CBDCA has an advantage over other therapy for acute leukemia because of its highly selective myelotoxicity and minimal gastrointestinal and renal toxicity. A standard phase II study should be undertaken to establish a more accurate response rate.