The aim of the present study was to evaluate the clinical role of bronchoscopic and nonbronchoscopic bronchoalveolar lavage (BAL) in the diagnosis of infectious and interstitial lung disease in children. BAL was performed using three 1 mL.kg-1 aliquots of normal saline, with the flexible bronchoscope (Olympus 3.6 or 4.8 mm) wedged in a segmental or subsegmental bronchus of the lobe that showed most abnormality on chest radiograph. In seven children with severe diffuse lung disease who were intubated, a nonbronchoscopic suction catheter lavage was performed. Fluid cultures and cellularity were evaluated using identical methods for both techniques. Between January 1993 and April 1994, 41 BAL were performed in 32 children aged 2 months to 17 yrs (median 8 yrs). Of these lavages, 14 were in heart and heart-lung transplant recipients, 11 in children known to be immunocompromised, and 16 in children who had a lung biopsy for interstitial lung disease or who had presumed infective lung disease. Transbronchial biopsies (TBB) or open lung biopsies were performed coincident with 19 BAL procedures. In all transplant recipients without clinical symptoms, BAL and TBB cultures were negative and BAL cellularity was normal. TBB did not reveal infection or rejection in any of these patients. A diagnosis of infection was made by BAL in 1 out of 8 transplant recipients with clinical symptoms, and a diagnosis of rejection was made by TBB in 3 out of 8 patients. In 6 out of 11 BAL in immunocompromised children, an infectious agent was found in the BAL fluid. In three other patients who had an open lung biopsy, an interstitial lung disease was diagnosed. In these patients, BAL was abnormal but not diagnostic. In summary, BAL proved helpful in the diagnosis of infective lung disease, but had little value in the diagnosis of rejection or parenchymal noninfective lung disease in children.