Alemtuzumab (marketed as Campath or Campath-1H) is a monoclonal antibody used in the treatment of chronic lymphocytic leukemia (CLL) and T-cell lymphoma.

Alemtuzumab targets CD52, a protein present on the surface of mature lymphocytes, but not on the stem cells from which these lymphocytes were derived. It is used as second line therapy for CLL. It was approved by the Food and Drug Administration for patients who have been treated with alkylating agents and who have failed fludarabine therapy.

A significant complication of therapy with alemtuzumab is that it significantly increases the risk for opportunistic infections, in particular, reactivation of cytomegalovirus.