Acute graft-versus-host disease (GVHD) has recently been associated with endothelial cell injury. The potential clinical significance was explored here in an autopsy review. Thirty-seven allogeneic bone marrow recipients were identified in the autopsy files at The Johns Hopkins Hospital with no evidence of systemic infection. Forty-one percent (15/37) of these patients were found to have extensive recent pulmonary hemorrhage at autopsy which was thought to have led to terminal respiratory failure and death. The 37 patients were divided into 2 groups: those with significant acute GVHD (stage 2 or greater) and those without GVHD (stage 0 or 1). Fifty-nine percent (10/17) of the patients with significant acute GVHD died of acute respiratory failure due to recent pulmonary hemorrhage as opposed to 25% (5/20) of those without acute GVHD (P = 0.032, Fisher's exact test). Terminal pulmonary hemorrhage was also associated with preparation for BMT, with 67% (12/18) of those prepared with total body irradiation (TBI) having pulmonary hemorrhage as opposed to 15% (3/19) of those prepared with chemotherapy using Busulphan (P = 0.002). There was no significant difference in posttransplant survival, engraftment, or final platelet count between the patients stratified by GVHD or preparative protocol. The data support a strong association between significant acute GVHD and terminal hemorrhage, as well a possible association between TBI and pulmonary hemorrhage. Analysis of variance demonstrates that GVHD and TBI are independently associated with increased pulmonary hemorrhage (P < 0.01 for GVHD, P < 0.001 for TBI). We propose that GVHD contributes to terminal pulmonary hemorrhage by injuring the endothelium. However, this association could also be a secondary effect, i.e., toxicity from therapy for GVHD, or an abnormality in cytokines or growth factors. The pathogenic relationship between significant GVHD and terminal hemorrhage is discussed briefly.