Fludarabine can exacerbate idiopathic thrombocytopenia (ITP) in chronic lymphocytic leukemia (CLL). We report 3 CLL patients with refractory fludarabine-associated ITP who responded to rituximab. The patients had Rai stages III, III, and IV disease. Before fludarabine treatment, the platelet counts were 141 000/microL, 118 000/microL, and 70 000/microL. ITP developed within week 1 of cycle 3 in 2 patients and within week 2 of cycle 1 in 1 patient. Platelet count nadirs were 4000/microL, 1000/microL, and 2000/microL, respectively, and did not respond to treatment with steroids or intravenous immunoglobulin. Rituximab therapy (375 mg/m(2) per week for 4 weeks) was begun on days 18, 23, and 20 of ITP. Patient 1 achieved a platelet count of more than 50 000/microL at day 21 and more than 133 000/microL at day 28, patient 2 achieved a platelet count of more than 50 000/microL at day 4 and more than 150 000/microL at day 10, and patient 3 achieved a platelet count of more than 50 000/microL at day 5 and 72 000/microL at day 28 of rituximab therapy, with platelet response durations of 17+, 6+, and 6 months. These results suggest rituximab can rapidly reverse refractory fludarabine-associated ITP.