Experimental work in animal models suggests that the course of systemic and organ-specific autoimmune disorders can be modified by allogeneic bone marrow transplantation (BMT). We describe two patients, each with a long history of psoriasis and ulcerative colitis, who received an allogeneic BMT for leukaemia. Four years post-BMT, they remain in full remission of psoriasis and ulcerative colitis, and of their leukaemia. We review the evidence for support of the concept that both psoriasis and ulcerative colitis are immune-mediated disorders and speculate on the possible role of allogeneic BMT in treating life-threatening autoimmune disorders.