BACKGROUND--Despite the immune suppression, frequent hospital admissions, and many intercurrent illnesses associated with HIV infection, Pseudomonas aeruginosa has been cited relatively infrequently as a respiratory pathogen in HIV positive patients. METHODS--The microbiological isolates, medical records, radiographic reports, and laboratory data from 224 patients undergoing sputum induction and/or bronchoalveolar lavage for evaluation of respiratory symptoms suspicious for Pneumocystis carinii pneumonia (PCP) from 1989 to 1992 were reviewed retrospectively. RESULTS--An increasing number of respiratory isolates with Pseudomonas aeruginosa was found over this time period. Eighteen of the 224 patients were identified in whom P aeruginosa was recovered on at least one occasion. These patients were more likely to have a history of smoking and prior PCP than those in whom Pseudomonas was not recovered. Mean CD4 counts were also significantly lower in these patients. CONCLUSIONS--Pseudomonas aeruginosa may be recovered from a substantial number of respiratory isolates from HIV positive patients suspected of having PCP. The prevalence of this phenomenon may be increasing.