The pathological lesions found in 68 successfully engrafted patients with human leucocyte antigen-matched sibling-related bone marrow transplants werereviewed retrospectively. Twenty-six (38%) patients had acute graft-versus-host disease, which was slightly less than that reported in Caucasians. Skin was a constant site of involvement (100%), followed by the gastrointestinal tract (74%) and liver (59%). There was a 74% correlation between the clinical and histological grading of cutaneous graft-versus-host disease, while that of the gastrointestinal tract was lower at 60%. Cytomegalovirus colitis was found on histological examination of two patients clinically thought to have graft-versus-host disease. Histological evidence of infection, which included viral hepatitis (n=5), disseminated cytomegalovirus infection (n=3), disseminated aspergillosis (n=2), systemic candidiasis (n=2), Pneumocystis carinii pneumonia (n=1), and bacterial pneumonia (n=1), was present in 14 patients. In addition to graft-versus-host disease and infections, there was a case of veno-occlusive disease of the liver. Histological examination is important in distinguishing graft-versus-host disease from infection and other complications in bone marrow transplantation.