An autopsy case of disseminated Trichosporon beigelii infection in a patient with acute promyelocytic leukemia is presented. We diagnosed the T beigelii infection with immunoperoxidase method using our rabbit antiserum to T beigelii. The diagnosis of T beigelii infection is difficult, because of its close resemblance to Candida species in both clinical features and histopathologic findings. We could consistently identify T beigelii in tissue sections with the present immunohistologic method. We conclude that the immunoperoxidase method using antiserum to T beigelii is very useful to diagnose T beigelii infection.