To determine the utility of bone marrow examination for the diagnosis of opportunistic infections and lymphoma in patients with known or suspected human immunodeficiency virus (HIV) infection, we retrospectively reviewed the medical and laboratory records of all patients undergoing diagnostic bone marrow examinations at San Francisco General Hospital between January 1, 1988 and December 31, 1989. All marrow examinations of patients with known or suspected HIV infection in which specimens were examined histopathologically and/or microbiologically for opportunistic pathogens or lymphoma were analyzed. Bone marrow examination resulted in the diagnosis of mycobacterial infection in 16% of the patients studied. Blood culture was 77% sensitive and bone marrow culture was 86% sensitive for detecting disseminated mycobacterial infection. This difference was not statistically significant (p greater than 0.05). Disseminated fungal infections occurred in less than 5% of the patients studied, and most were rapidly and accurately detected by examination of stained bone marrow samples. No case of lymphoma was diagnosed by bone marrow examination. Bone marrow examination may be useful for diagnosing opportunistic infections in patients with HIV infection. Mycobacterial blood cultures have a sensitivity comparable to bone marrow cultures in detecting disseminated mycobacterial infections, are less invasive, and may be less costly. Marrow examination is not useful for diagnosing lymphoma but can determine the extent of lymphoma that has been diagnosed by other means.