We studied the effect of alcohol ingestion on sleep-induced breathing abnormalities and arterial oxyhaemoglobin saturation in seven patients with a range of sleep-induced upper airway occlusion. The characteristics of each patient's sleep-induced breathing abnormality was established on one or more control all-night studies, and then a further all-night study was done immediately following alcohol ingestion. Alcohol increased the duration and frequency of the occlusive episodes in five patients with obstructive sleep apnoea, and resulted in a marked increase in the degree of hypoxaemia in the first hour of sleep. In two patients with benign chronic snoring, alcohol induced frank obstructive sleep apnoea during the first hour of sleep. We suggest that the increased tendency to develop obstructive apnoea after alcohol is the result of alcohol-induced oropharyngeal muscle hypotonia, while the increased duration of obstructive apnea is the result of alcohol-induced depression of arousal mechanisms.