Previous work has demonstrated that the urine from mature female salmonids contains a priming pheromone that significantly enhances the reproductive physiology of receiving males. The chemical identity of the pheromone(s) has not yet been identified. The present study investigated the possibility that F-type prostaglandins (PGFs) may have a pheromonal role in Atlantic salmon by measuring the olfactory sensitivity of male salmon to PGFs, the effect of waterborne PGFs on male reproductive physiology and the PGF content of mature female urine. Electrophysiological studies demonstrated that the olfactory epithelium of mature male salmon parr was acutely sensitive to PGF1[alpha] and PGF2[alpha], with detection threshold concentrations of 10(-11) mol l-1. The olfactory epithelium was also sensitive to the PGF metabolite 15-ketoPGF2[alpha] (threshold 10(-8) mol l-1), but did not detect a further metabolite, 13,14-dihydro-15-ketoPGF2[alpha]. Sensitivity to both PGF1[alpha] and PGF2[alpha] increased as the reproductive season progressed. Exposure of mature male parr to waterborne PGF1[alpha] and PGF2[alpha] (10(-8) mol l-1) resulted in significant increases in levels of expressible milt and in the plasma concentrations of 17,20ss-dihydroxy-4-pregnen-3-one, testosterone and 11-ketotestosterone. Urine from ovulated female salmon also contained large quantities (18 ng ml-1) of immunoreactive PGFs, whereas urine from mature males and non-ovulated mature females contained significantly smaller amounts (<1 ng ml-1). The results support the theory that PGFs function as priming pheromones in Atlantic salmon and are released in the urine of ovulated female salmon. The involvement of these pheromones in synchronising male-female salmon spawning is discussed.