The development of GVHD following allogeneic BMT is known to be closely associated with significant antileukaemic activity. Immunological graft-versus-leukaemia (GVL) effects are now well established and are commonly exploited in the treatment of leukaemic relapse following allogeneic transplantation by the use of donor lymphocyte infusions. More recently a graft-versus-myeloma (GVM) effect following allogeneic transplantation has been documented, suggesting that eradication of haematological malignancies following allogeneic transplantation is achieved at least in part by immunological mechanisms. It is now also established that spontaneous GVHD can occur following autologous transplantation and can be induced by cyclosporin A administration. However, there is only limited evidence that the development of autologous GVHD has an antitumour effect. We report for the first time the development of autologous GVHD following PBSC transplantation for myeloma apparently resulting in a GVM effect.