In the attempt to induce graft-vs-host disease (GVHD) in patients undergoing autologous bone marrow transplantation (ABMT) or blood stem cell transplantation (BSCT), 12 consecutive patients received cyclosporin A (CyA) post transplant. CyA was given at a dose of 1.5 mg/kg/day intravenously for 28 days, starting on the day of transplant. Histologically proven acute GVHD of the skin occurred in seven patients 9-14 days after ABMT and lasted 7-11 days. CyA-induced GVHD after ABMT resembles mild GVHD after allogeneic bone marrow transplantation (BMT). Although the preliminary data reported here show that it is possible to induce GVHD in patients undergoing ABMT, it is not yet known whether GVHD after ABMT will have an antitumor activity.