Snoring is an extrathoracic inspiratory airway obstruction during sleep, accompanied by more or less intense noise. The inspiration volume being limited at the same time, this can produce additional blood gas changes. Epidemiological studies have shown an increased risk of myocardial infarction or cerebral ischaemia during night for snorers. Little is known, however, about acute effects of snoring on the haemodynamics of heart and circulation. The present study presents data of the pulmonary artery blood pressure during sleep-related upper airway obstruction. Pulmonary arterial pressure during sleep was examined with five patients via Swan-Ganz catheter. When an upper airway obstruction occurred, the inspiratory pulmonary arterial pressures rose in all the five patients. Two patients showed a clinically significant decrease in arterial oxygen saturation during snoring so that in these cases, a hypoxic vasoconstriction can be discussed as a possible cause. The other three patients did not produce significant decreases in oxygen saturation, so that in these cases mechanical factors (negative inspiratory intrathoracic pressure oscillations) should be regarded as the most probable cause for increases in the pulmonary arterial blood pressure.