Chronic bibasilar alveolar infiltrates existed for more than 2 years in a 25-year-old woman infected with HIV for more than a decade. Bronchoscopically, there were copious, purulent secretions that grew methicillin-resistantStaphylococcus aureus(MRSA). Transbronchial biopsy specimens demonstrated plasma cell interstitial pneumonia (PCIP). Focal, transient radiographic improvement occurred after antistaphylococcal antimicrobial therapy. With recurrent and progressive symptoms, sustained clinical and radiographic improvement did not occur until corticosteroid therapy was instituted with tuberculosis chemoprophylaxis. Persistent antigenic stimulation in immunosuppressed patients causes PCIP. In this instance, the stimulus is MRSA. The previous model and support for this theory isPneumocystis carinii. There is good experimental reason for a plasma cell response in persons infected with HIV. To our knowledge, this is the first case of chronic plasma cell interstitial pneumonia caused by indolent MRSA infection.