The present study was designed to investigate the effect of cooling on the modulatory role of the respiratory epithelium on the underlying smooth muscle. Canine bronchial rings and segments (with or without epithelium) were suspended in organ chambers and perfused with modified Krebs-Ringer bicarbonate solution, respectively. Isometric force was recorded. Cooling did not affect the resting tension of the bronchi. During contractions to carbachol, cooling evoked contractions in bronchi with epithelium but relaxations in those without epithelium. In the presence of indomethacin, cooling induced contractions in both preparations with and without epithelium. The contractions in bronchi with epithelium were significantly larger than those in bronchi without epithelium. After treatment with indomethacin, exogenous arachidonic acid potentiated the cooling-induced contractions in preparations with epithelium but not in those without epithelium. This potentiation was not affected by nordihydroguaiaretic acid. SKF 525-A and metyrapone, inhibitors of cytochrome P-450 monooxygenases, converted the cooling-induced contractions of preparations with epithelium to relaxations and had no significant effects on the responses of preparations without epithelium. These observations suggest that cooling induces from the epithelium the release of a cytochrome P-450-derived eicosanoid that potentiates contractions of the underlying airway smooth muscle to carbachol.