Monoclonal antibodies are receiving ever-increasing utilization in the treatment of hematologic malignancies. Campath-1 antibodies are directed against the surface antigen CD52 that is expressed on virtually all lymphocytes and monocytes. Murine forms, Campath-1G and Campath-1M, have been utilized extensively in allogeneic bone marrow transplants in order to purge the allograft of lymphocytes. The humanized form, Campath-1H, is currently the focus of many clinical trials in hematologic malignancies and autoimmune diseases. The genetically engineered Campath-1H has been utilized in the treatment of lymphomas and lymphoid leukemias with impressive results. T-cell prolymphocytic leukemia, chronic lymphocytic leukemia, and non-Hodgkin lymphomas appear to be particularly good targets for this agent. Campath-1H may be administered intravenously or subcutaneously. Infectious complications are the most significant side effect associated with its usage, with fevers, chills, nausea, and vomiting most common. Antibiotic prophylaxis has made the infectious morbidity associated with Campath-1H more manageable. The efficacy demonstrated in clinical trials and manageable toxicities make Campath-1H an appealing agent in the treatment of hematologic malignancies.