This multicenter phase 2 trial investigated safety and efficacy of a new immunochemotherapeutic regimen combining rituximab (R) and fludarabine (F) in patients with fludarabine- and anthracycline-naive chronic lymphocytic leukemia (CLL). The rationale for using R + F includes single-agent efficacy of both drugs, in vitro synergism of R and F, and no apparent overlapping toxicity. Of 31 eligible patients with B-CLL enrolled, 20 were previously untreated and 11 relapsed. Treatment consisted of fludarabine administered at standard doses (25 mg/m(2)/d; days 1-5, 29-33, 57-61, and 85-89) and rituximab (375 mg/m(2)/d) given on days 57, 85, 113, and 151. Side effects such as fever, chills, and exanthema were generally mild (National Cancer Institute Common Toxicity Criteria [NCI-CTC] grade 1/2 in 48% and grade 3 and/or 4 in 3% of patients). Fever and chills were mainly associated with the first rituximab infusion. Hematologic toxicity included neutropenia (grade 1 and/or 2 in 26%, grade 3 and/or 4 in 42%) and thrombocytopenia (grade 1 and/or 2 in 19%, grade 3 and/or 4 in 9%). One patient died of cerebral bleeding during prolonged thrombocytopenia after the second cycle of fludarabine. There were a total of 32 infections in 16 patients, none of which was fatal. The overall response rate (complete remission [CR] and partial remission [PR]) was 87% (27 of 31 evaluable patients). In 20 previously untreated patients, 17 (85%) responded. Ten of 31 patients achieved CR (5 of 20 untreated; 5 of 11 pretreated; 9 of 21 Binet stage B, 1 of 10 Binet stage C). The median duration of response was 75 weeks. We conclude that the combination of rituximab and fludarabine is feasible and effective in patients with B-CLL.