Exposure of phosphoramidon-treated (0.1 mM solution by aerosol for 15 min) guinea pigs to an aerosol of endothelin-1 (ET-1) (10 micrograms/ml) for 30 min induced after 18-24 h an enhanced bronchopulmonary response (BR) to rechallenge with ET-1 (3 micrograms/ml) administered by aerosol. Compared with saline-exposed animals, aerosol exposure of guinea pigs to ET-1 (10 micrograms/ml) for 30 min did not alter the dose-related BR to acetylcholine (ACh) administered by aerosol 18-24 h following challenge with the peptide. In phosphoramidon-treated guinea pigs, ET-1 (5 micrograms/ml) exposure for 30 min evoked a slight but non-significant enhancement of the ACh-induced BR. Administered by aerosol in phosphoramidon-treated guinea pigs, ET-1 did not induce eosinophil accumulation in the lung, as demonstrated by examination of histological preparations and the assessment of the cell composition of bronchoalveolar lavages. The present data indicate that in spite of treatment of guinea pigs with phosphoramidon, ET-1 administration does not lead to the development of bronchial hyperresponsiveness.