BACKGROUND The use of fludarabine, an analog of vidarabine with significant lymphocytolytic activity, has provided encouraging results in the treatment of patients with non Hodgkin's lymphoma (NHL) and sometimes in phase II studies of solid tumors and acute leukemias. Fludarabine has also been shown to be effective in B-CLL. Some studies referred results using fludarabine in high-risk untreated or pretreated CLL patients. METHODS We report treatment results with fludarabine and prednisone in 22 pretreated B-CLL patients in progressive disease, refractory to CHL and other regimens. RESULTS One patient obtained a complete response (CR), 8 obtained a partial response (PR). Thirteen failed to respond to treatment. Among the partial responders, 1 patient had fatal pneumonia while neutropenic, another died of disease progression. Among the non responders, 7 died of progressive disease, and 3 evolved into high-grade NHL. Three are still alive in disease progression. CONCLUSIONS We confirm the effectiveness of fludarabine in pretreated and resistant B-CLL, but in the light of the considerable toxicity observed in this series, we believe that the drug would be better employed as a first-line approach to "younger" untreated B-CLL patients.