Guinea-pig tracheae were cut into transverse strips or spirals and although there is only minor difference in the angle of cut, the former preparations relaxed in response to ATP and adenosine while the latter contracted. Theophylline antagonised both types of response suggesting involvement of P1-purinoceptors. Dipyridamole potentiated inhibitory responses to ATP and adenosine in transverse strips but reversed contractile responses to ATP and adenosine in spiral strips. Antagonism of contractions to ATP and adenosine in spiral strips by hyoscine is consistent with an action of adenosine on cholinergic nerves. The likelihood that ATP rapidly forms adenosine by which it acts is discussed.