Few reports are available on the treatment of patients with Waldenström macroglobulinemia (WM) and primary or secondary resistance to alkylating-agent-based regimens. From December 1993 through December 1997, 92 patients with WM resistant to first-line therapy (42) or with first relapse (50) after alkylating-agent therapy were randomly assigned to receive fludarabine (25 mg/m(2) of body-surface area on days 1-5) or cyclophosphamide, doxorubicin (Adriamycin), and prednisone (CAP; 750 mg/m(2) cyclophosphamide and 25 mg/m(2) doxorubicin on day 1 and 40 mg/m(2) prednisone on days 1-5). The first end point evaluated was the response rate after 6 treatment courses. Forty-five patients received CAP and 45 received fludarabine. Two patients died before the first course of chemotherapy. No statistical differences were observed between the 2 treatment arms with respect to hematologic toxicity or infections. Mucositis and alopecia occurred significantly more often in patients treated with CAP. Partial responses were obtained in 14 patients (30%) treated with fludarabine and 5 patients (11%) treated with CAP (P =.019). Responses were more durable in patients treated with fludarabine (19 months versus 3 months), and the event-free survival rate was significantly higher in this group (P <.01). Forty-four patients died, 22 in the fludarabine group and 22 in the CAP group. There was no statistical difference in the median overall survival time in the 2 study arms. Fludarabine was thus more active than CAP in salvage therapy of WM and should be tested as first-line therapy in a randomized comparison with alkylating agents.