We report on two patients with chemoresistant B-cell chronic lymphocytic leukemia who were treated successfully with the monoclonal anti-CD 20 antibody rituximab. Both patients suffered from severe thrombocytopenia requiring platelet transfusions over a period of several months. Neither chemotherapy nor immunosuppressive agents (corticoids, immunoglobulins) were effective. After four doses of rituximab (375 mg/m2 weekly), both patients recovered within a few weeks to hematological partial remission. One patient was re-treated successfully three times after relapses. Both patients were premedicated with prednisone (100 mg) 30 min prior to the infusion to prevent cytokine release and the antibody infusions were well tolerated.