Treatment with antibodies in patients with lymphoproliferative diseases was, until recently, limited to phase I studies due to limited response or subsequent development of anti-globulin response. The introduction of the hybridoma technique during the 1970s facilitated large scale production of antibodies, including the development of the Campath rat-antibodies. The epitope was launched against CD52, a glycoprotein present in large amounts on the surface of lymphocytes, and the primary use was in-vitro depletion of bone marrow from allogeneic bone marrow transplantation donors. The development of the human Campath-1H antibody was successful in 1988, leading to minimized anti-globulin response when used in vivo, and large multi-center studies were initiated. In this study we present an overview of the preclinical and clinical experiences with Campath-1H, including data from patients treated with the antibody in our clinic.