TB is common in the setting of HIV-induced immunosuppression, especially among demographic groups with a high background prevalence of tuberculous infection. It is often the first (sentinel) infectious disease to appear, extrapulmonary and disseminated disease is common, the chest x-ray picture is frequently atypical, and the tuberculin skin test is often falsely negative. It therefore requires a high index of suspicion and an aggressive diagnostic approach to avoid missing HIV-related tuberculous disease, which is communicable from man to man by the aerosol route and which appears to be highly treatable with conventional anti-TB drugs. Identification and INH prophylaxis of tuberculous-infected, HIV-seropositive persons is likely to be very important in the prevention of tuberculous disease. MAI is also a very common pathogen that frequently produces extrapulmonary and disseminated disease among patients with AIDS. In contrast to TB, AIDS-related MAI disease occurs more uniformly among the AIDS risk groups, occurs late among the HIV-related infections, and is not effectively treated with current drug regimens.