Central hemodynamics and blood gases were measured continuously during flexible fiberoptic bronchoscopy performed under topical anesthesia in ten patients with restrictive lung disease. The procedure induced marked hemodynamic changes, which were maximal and similar in magnitude, during passage through the larynx and during suctioning. Mean arterial pressure increased by 30 percent, heart rate by 43 percent, cardiac index by 28 percent and mean pulmonary arteriolar occlusion pressure by 86 percent compared with pre-bronchoscopic control values. A slight fall in arterial oxygen tension was measured during bronchial suctioning and in the post-bronchoscopic period. Rate pressure product reached its highest value during bronchial suctioning at which time three of the ten patients developed ST-T-segment changes, implying that myocardial oxygen demand might have exceeded supply. It is suggested that the major mechanism behind the hemodynamic changes is a reflex sympathetic discharge caused by mechanical irritation of larynx and bronchi.