Campath-1H is an unconjugated, humanized monoclonal antibody directed against the CD52 antigen present on B cells, as well as T cells and other mononuclear cells. In phase II trials, this antibody has shown impressive activity in chronic lymphocytic leukemia (CLL) and T-cell prolymphocytic leukemia (T-PLL) but limited activity in NHL (Österborg et al: J Clin Oncol 15:1567-1574, 1997; Pawson et al: J Clin Oncol 15:2667-2672, 1997; Lundin et al: J Clin Oncol 16:3257-3263, 1998). In CLL, responses to Campath-1H have been reported in 30% to 70% of patients who had not responded to prior treatment, including fludarabine (Fludara), with complete response (CR) rates ranging from 4% to 50%. More than two-thirds of T-PLL patients have achieved CRs, but these do not seem to be durable. Only 14% of patients with low-grade NHL achieved partial responses (PRs), although responses were noted in about half of a small number of patients with mycosis fungoides.