Since July 1988, a total of 92 transbronchial biopsies (TBB) have been performed in 18 patients (aged 3-16 years). Twelve patients (67%) were heart-lung transplant (HLT) recipients undergoing surveillance for pulmonary graft rejection and infection. The remainder included immunocompromised patients at risk of opportunistic infections (n = 4), patients with fibrosing alveolitis (n = 1) and a collagen vascular disorder with suspected lung involvement (n = 1). TBB was performed through either a fiberoptic (n = 50) or a rigid (n = 41) bronchoscope, all under general anesthesia. On one occasion a cardiac bioptome was used through an endotracheal stent. The sensitivity of TBB for diagnosing acute and chronic rejection in HLT patients was 88% and 60%, respectively (specificity, 91% and 100%). Definitive diagnoses were made in 4 (67%) of the non-HLT group. Bronchoalveolar lavage (BAL) was performed during each procedure for microbiological and cytological examination. Thirty-four pathogenic organisms including Pseudomonas aeruginosa (16/34), Staphylococcus aureus (8/34), and Candida albicans (5/34) were isolated from BAL culture. Complications included pneumothorax (8%), transient pyrexia (7%), and dyspnea (2%).