One hundred and twenty consecutive bronchoscopic examinations were carried out on 80 patients with acquired immune deficiency syndrome (AIDS) between January 1982 and December 1986. Ninety one paired biopsy and cytology specimens from 72 of these patients were analysed. There was no significant difference between biopsy and cytology in diagnosing Pneumocystis carinii pneumonia (0.95 greater than p greater than 0.1). In 10 cases P carinii pneumonia was diagnosed by biopsy but not cytology and in seven cases by cytology but not biopsy. Nineteen patients had multiple infections or Kaposi's sarcoma. Biopsy was more useful than cytology in the diagnosis of other infections (n = 20) and Kaposi's sarcoma (n = 2) with positive cytological correlation in only three of the infections. Biopsy and cytology together have a diagnostic yield of 78.3%. We conclude that all patients presenting with respiratory disease who have, or are in a high risk group for, AIDS should be examined by bronchoscopy at an early stage with both cytology and biopsy.