We studied the effects of prostaglandin E2 (PGE2) on the contractile responses of in vitro guinea pig tracheal preparations with intact vagal innervation. The preparation was stimulated either through the vagal nerves (NS) or with an electrical field (EFS) and trachealis response was assessed from the pressure change inside the tracheal tube. Ganglionic blockade by hexamethonium inhibited responses to NS but did not affect EFS while both responses to NS and EFS were abolished by atropine or tetrodotoxin. This indicates that responses to both stimulation modalities were mediated by cholinergic nerves but that NS involved a ganglionic relay whereas EFS did not. Within the frequency range of 0.1-20 Hz, there was a gradual increase in the pressure generated by the trachealis muscle with increasing frequency of stimulation. The frequency-response relationship was similar for NS and EFS. Thus, the ganglion does not appear to play an important filtering or amplifying role under those conditions. PGE2 (1-50 mM) produced a concentration-dependent inhibition of NS and EFS without affecting responses to exogenous acetylcholine (ACh). This suggests that the main action of PGE2 is to reduce ACh release from post-ganglionic nerve terminals. PGE2 inhibited EFS to a larger extent than NS; we postulate a possible excitatory effect of PGE2 on neurotransmission in the airway ganglia.