During a six-month period, 40 consecutive fiberoptic bronchoscopic procedures including bronchoalveolar lavage, bronchial brushing and forceps biopsy were performed in local anaesthesia on 34 HIV-infected males presenting symptoms compatible with Pneumocystis carinii pneumonia. In 23 examinations, P. carinii was found. Sixteen examinations were non-diagnostic and one was unsuccessful. The clinical course confirmed the diagnoses of the P. carinii positive as well as the P. carinii negative patients. Except for a lower total lymphocyte count in the patients harbouring P. carinii, the two groups did not differ with regard to history, clinical examination, immunology, serology or chest radiograph. We conclude that fiberoptic bronchoscopy should be performed on wide indications in HIV-infected patients with symptoms compatible with P. carinii pneumonia. The procedure is easily performed, it is safe, and it is highly sensitive. The advantage of an early diagnosis compensates for a rather high frequency of negative examinations.