Asthma is a chronic inflammatory disorder of the airways in which many cells participate. This inflammation causes recurrent episodes and symptoms that are associated with widespread but variable airflow limitation that is at least partly reversible either spontaneously or with treatment. Therefore, an investigation of useful remedies for the treatment of bronchial asthma is proposed. In this study, we determined whether both forms of pituitary adenylate cyclase activating polypeptide (PACAP 38 and PACAP 27) belonging to the vasoactive intestinal peptide (VIP) family of peptides could inhibit the effects of histamine-induced respiratory resistance (Rr) in anesthetized guinea pigs, when compared with VIP. The order for 50% suppression (ED50) of Rr induced by peptides was VIP > PACAP 27 > PACAP 38. The inhibitory effects induced by PACAP 38 on histamine-induced Rr in guinea pigs were more prolonged than with the other two peptides. Moreover, adding the endopeptidase inhibitor phosphoramidon prolonged the inhibitory effects of PACAPs. These results suggested that the exogenous peptides of the inhibitory nonadrenergic noncholinergic nervous (i-NANC) peptides could become a useful remedy for treatment of bronchial asthma, because these belong to an important intrinsic hormone.