Almitrine stimulates breathing by activating peripheral chemoreceptors and was given orally in a dose of 200 mg/day to nine patients with sleep apnoea syndrome, after a single blind placebo sequence. No reduction in the number of respiratory events per hour of sleep was observed. On the other hand Almitrine led to a significant fall in the mean duration of respiratory events (p less than 0.02). This fall occurred principally in the obstructive apnoea group and in those with mixed apnoea only during light slow wave sleep. These results are in agreement with the hypothesis that the arousal response to hypoxia mediated by the chemoreceptors could be responsible for the termination of sleep apneas.