Fludarabine 25 mg/m2 was given on five consecutive days every four weeks to 85 patients with B- and T-cell malignancies. The median number of courses given was five. All patients except one had received previous chemotherapy. The overall response rate in non-Hodgkin's lymphoma (NHL) was 50% (five complete responses (CR) and 19 partial responses (PR)). The response rate in chronic lymphocytic leukemia (CLL) was 43% (four CR and 12 PR). Responses were seen in all groups of B-cell malignancies, but no T-cell malignancies (n = 4) responded. The median duration of CR has not been reached and the median duration of PR was 14 months for NHL and 16 months for CLL. The median survival from starting fludarabine for patients who achieved a CR or PR in NHL has not been reached and the median duration of PR in CLL was 23 months. The median duration of survival in non-responders was five months. Fludarabine was well tolerated and the main toxicity was myelosuppression. Our results suggest that even in patients who have never responded to any chemotherapy, regardless of the number of treatment regimens previously given, there is a 36% chance of response. In addition, this is the first report of fludarabine activity in Franklin's disease.