Tongue ulcerations in seven patients who had undergone allogeneic BMT for hematologic or lymphoid malignancies were examined for the presence of CMV. The clinical presentation of these tongue lesions was nonspecific and showed ulcerations similar to those associated with severe preparative conditioning regimen-related mucositis, HSV infection and oral acute GVHD. Tissue biopsies were studied by routine histology, immunocytochemistry for CMV and HSV antigens, in situ hybridization for CMV nucleic acid and standard as well as centrifugation viral cultures. Five of the 7 patients had lesions which were positive for CMV. While CMV oral lesions are known to occur in patients with the acquired immune deficiency syndrome (AIDS), these findings will improve our ability to recognize and diagnose tongue lesions in BMT patients and indicate that CMV should be considered in the differential diagnosis for similar ulcerations in other immunocompromised patients.