In anesthetized dogs, almitrine (0.5-3 mg/kg i.v.) induced a dose-dependent increase in respiratory rate and ventilation. The aortic and carotid chemoreceptors were involved in the effects of almitrine. Section of both carotid sinus nerves and vagus nerves abolished the effects of the drug on respiration. The respiratory response did not occur in dogs with bilateral lesions of the nucleus of the solitary tract. The electrical activity of chemoreceptor fibres was increased. Perfusion of almitrine into the carotid artery stimulated respiration. Inhalation of pure oxygen shifted the dose-response curve of the respiratory effect towards the right. Almitrine slightly stimulated ventilation in dogs with bilateral section of carotid sinus nerves and aortic nerves and this disappeared when both vagus nerves were cut indicating that this effect was mediated through some chemoreceptor fibres present in the vagus nerves or through afferent vagal fibres.