We report the efficacy and safety of intravenous low-dose alemtuzumab (10 mg three times weekly for 10 weeks) in 12 patients with relapsed or refractory chronic lymphocytic leukemia. Low-dose alemtuzumab induced significant responses in these patients (16% complete remission, 25% partial remission), with mild hematologic and extrahematologic side effects and a low rate of infections, even in the presence of long-lasting severe immunosuppression.