We investigated the effect of rigid bronchoscopy used together with flexible bronchoscope, on arterial blood gases, in 20 cases. When the two bronchoscopes were used together there was a significant decrease in partial arterial oxygen pressure (PaO2). After broncho-alveolar lavage the decrease of PaO2 was more remarkable. But it was less compared with cases which fiberoptic bronkoscope was applied. Insignificant changes were observed in partial arterial carbondioxide values.