Adult T-cell leukemia-lymphoma (ATL) is resistant to currently available chemotherapy and has a poor prognosis. We describe here a patient with ATL successfully treated with 2-chlorodeoxyadenosine (2-CdA). A 75-year-old Japanese male with an acute type of ATL, who had become resistant to the initial cytotoxic chemotherapy, was treated with 2-CdA administered by continuous drip infusion of 0.09 mg/kg/d for seven consecutive days in one month (one cycle). After three cycles of treatment, partial remission (PR) was achieved. Surprisingly, 249 days after the administration of 2-CdA, ATL cells completely disappeared from the peripheral blood. PR was maintained during 10 weeks until evidence of a new lymphadenopathy. No remarkable toxicity of 2-CdA occurred.