Bendamustine demonstrated clinical activity in pre-treated hematological malignancies due to its unique mechanism of action distinct from standard alkylating agents. This study assessed its efficacy in patients with chronic lymphocytic leukemia pre-treated with an alkylator, in comparison to fludarabine. Patients with relapsed chronic lymphocytic leukemia requiring treatment after one previous systemic regimen (usually chlorambucil-based) were randomized to either receive bendamustine 100 mg/m(2) on days 1 and 2 of a 4-week cycle or standard fludarabine treatment consisting of 25 mg/m(2) on days 1 to 5 every 4 weeks. The primary objective was to achieve non-inferior progression-free survival (PFS) with bendamustine. Out of a total of 96 patients randomized, 92 were eligible, 49 allocated to bendamustine and 43 to fludarabine. About half of the patients received six or more cycles. Overall response rates were 76 % on bendamustine and 62 % on fludarabine, with clinical complete response rates of 27 and 9 %, respectively. Median PFS was 20.1 and 14.8 months (hazard ratio, 0.87; 90 % confidence interval, 0.60-1.27), median overall survival 43.8 and 41.0 months (hazard ratio, 0.82). Thrombocytopenia and gastrointestinal toxicities were marginally more frequent on bendamustine, albeit CTC grade 3/4 event incidence was similar. These data suggest at least comparable efficacy of bendamustine vs. fludarabine, pointing to an alternative treatment option in relapsing CLL patients after chlorambucil containing initial chemotherapy.