The effect of human recombinant interleukin-1β (IL-1β) on the contractile responses of canine airway smooth muscle to acetylcholine (ACh) was studied under isometric conditions in vitro. Exposure of bronchial rings to IL-1β for 4h but not for 15 min decreased the ACh-induced contraction in a dose-dependent fashion. This inhibitory effect was not altered by indomethacin or propranolol, but was eliminated by pretreatment with cycloheximide. These results suggest that IL-1β inhibits airway smooth muscle contraction through protein synthesis.