A late phase II study of a new camptothecin analogue, irinotecan hydrochloride (CPT-11), was conducted to evaluate the anti-tumour effect and toxicity in patients with refractory leukaemia and lymphoma including adult T-cell leukaemia (ATL)-lymphoma, in a multi-institutional cooperative study. All the patients with ATL had been previously treated with various conventional combination chemotherapies and were refractory to these therapies or had relapsed. CPT-11 was administered at a dose of 40 mg m-2 day-1 for three consecutive days repeated weekly until evidence of disease progression. One complete remission and four partial remissions were achieved in 13 assessable patients with ATL. The median total dose to achieve remission was 240 mg m-2 and the median duration of response was 31 days. The major toxicities were leucopenia (83%), diarrhoea (62%) and nausea/vomiting (69%). These were relatively severe, but they were generally tolerable and reversible. However, one patient died probably as a result of this therapy. No effective chemotherapy for adult T-cell leukaemia-lymphoma has yet been established, and the prognosis for patients with this disease is very poor. Our results suggest that CPT-11 may be a promising agent for this disease. Further combination therapy with CPT-11 is needed to improve the therapy for ATL.