2-Chlorodeoxyadenosine (2-CdA) is a purine analogue which has proved to be active in acute myeloid leukemia (AML), especially in children. In adults, results yielded by 2-CdA alone or with ara-C were less encouraging. Here we report on the efficacy of 2-CdA with or without daunorubicin (DNR) in 19 relapsing or refractory adult AML patients, with a median age of 57 years. 2-CdA was administered as a continuous infusion to all patients at a dose of 0.1 mg/kg per day for 7 days. For 14 patients, DNR was added at a dose of 50 mg/m2 per day on days 5, 6, and 7. Antileukemic activity was observed in all the patients, but no single complete remission was achieved. One patient had a long-lasting partial response (response rate=5%). The remaining patients died of progressive AML (n=7), uncontrollable infection with persistent disease (n=10), and cerebral hemorrhage (n=1). Median survival from start of 2-CdA therapy was 56 days. Long-lasting neutropenia and transfusion-dependent thrombopenia were encountered in all 16 evaluable patients. Grade 4 hepatic toxicity occurred in one patient. Other side effects included nausea in six, mucositis in three, and mental disturbances in three patients. Compared with 2-CdA alone, the addition of DNR to 2-CdA changed neither the response rate nor the toxicities. In conclusion, our data do not support the use of 2-CdA +/- DNR for relapsing or refractory adult AML patients, at least as used in the present regimen.