PURPOSE There is no consensus on the treatment of patients with Waldenström's macroglobulinemia (WM) who develop primary or secondary resistance to frontline therapies. We report our experience on the activity and toxicity of fludarabine in 71 patients with WM resistant to prior chemotherapy regimens. PATIENTS AND METHODS From January 1991 to June 1995, 71 patients were included in this retrospective study. The median age, median time from diagnosis to treatment, median immunoglobulin M (IgM) level, and median number of previous treatments were 68 years (range, 42 to 81), 5.9 years (range, 0.6 to 20), 35 g/L (range, 5 to 126), and two (range, one to four), respectively. RESULTS Seventy-one patients received a median of six courses of fludarabine. Twenty-one (30%) responded with a partial response and 50 (70%) were considered as treatment failures. Forty-six patients died: 10 in the responder group and 36 in the failure group. Twenty-five patients were alive with a median follow-up time of 34 months. The overall median survival time of all treated patients was 23 months. The time to treatment failure was 32 months. The only factor that favorably influenced the response to fludarabine was a longer interval between the first treatment and the start of fludarabine. Pretreatment factors associated with shorter survival in the entire population were hemoglobin level less than 95 g/L (P = .02) and platelet count less than 75 x 10(9)/L (P = .02). CONCLUSION The responses rate in this population with a poor prognosis is close to that reported in shorter series. Patients with WM who are resistant to alkylating agents should be identified early, so that salvage therapy with nucleoside analogs can be started without delay.