To the Editor: Alemtuzumab (Campath-1H) is a humanized anti-CD52 monoclonal antibody, the administration of which causes profound B- and T-lymphocyte depletion. It is licensed for use in the treatment of chronic lymphocytic leukemia, and it is increasingly used in the treatment of autoimmune diseases (particularly multiple sclerosis) and as an induction agent in renal transplantation. Although alemtuzumab is a potent immunosuppressant, several groups have described the paradoxical occurrence of autoimmune disease after its use, including thyroid disease and cytopenias. We describe two patients in whom anti–glomerular basement membrane disease developed after treatment with alemtuzumab. Patient 1 was a 40-year-old white . . .