One hundred consecutive patients, who underwent bronchoscopic examination for diagnostic purposes, were studied with regard to various aspects of possible SaO2 deterioration. Relevant findings are as follows: (1) The pulse oximeter is as good as the conventional blood gas analyser for quantitating SaO2; (2) oxygen desaturation in the range of 1 to 25 per cent (median 5, mean 5.6 +/- 4) occurred in approximately 97 per cent of the bronchoscopy examinees; recuperation time of SaO2 was 1 to 34 minutes (median 6, mean 8.2 +/- 6.5); (3) the factor aggravating desaturation included the examination of patients in the sitting position; the fact that bronchial washing was connected with greater SaO2 deterioration in the non-hypoxaemic group of patients needs further investigation with regard to its role in the mechanism of oxygen desaturation; (4) the amount of fluid instilled intra-tracheally, bronchial biopsy and duration of the procedure were not related to the decline in SaO2. Based on the results of the present study, the authors suggest that all procedures ought to be performed on patients undergoing examination in the supine position, and that the patients should be supplemented with low-flow oxygen.