A pleomorphic bacterium exhibiting both acid-fast rod forms and non-acid-fast coccal forms, and identified as Mycobacterium avium-intracellulare was cultured from a facial lesion diagnosed as immunoblastic sarcoma. The patient was a 36 year-old homosexual man who died of the acquired immune deficiency syndrome (AIDS). In addition, the patient had pre-existing cutaneous lesions of Kaposi's sarcoma (KS), and was treated for probable but never proven, Pneumocystis carinii pneumonia (PCP). Variably acid-fast coccoid forms, and extremely rare acid-fast rods were demonstrated within the microscopic sections of the immunoblastic sarcoma. Similar-staining coccoid forms were also observed within the microscopic sections of the pre-existing KS tumors, and within the lung biopsy material showing inflammation suggestive of PCP. These findings, along with previously reported findings of similar bacterial forms in vivo in other cases of KS and AIDS, again suggest that variably acid-fast bacteria may play a role in the development of malignant tumors and inflammatory lung disease, which frequently occur in homosexual men with AIDS.