Between October, 1985 and May 1987, 29 children (mean age 22 +/- 22 months, range 2-54 months) with AIDS or ARC developed acute respiratory illness. The initial diagnostic procedure was flexible fiberoptic bronchoscopy, with bronchoalveolar lavage (BAL). BAL was positive for Pneumocystis carinii in 14 and for respiratory syncytial virus, Staphylococcus aureus, and Escherichia coli in 3 additional patients. Subsequent lung tissue analysis and/or clinical course suggested no false negative lavages. Complications possibly related to the procedure occurred in two patients. We find BAL an effective diagnostic technique in these patients, offering a less invasive alternative to open lung biopsy.