GnRH-like substances have been isolated from interstitial fluid from the rat testis and have been found to exert direct, mainly inhibitory effects on steroidogenesis. In rat testis, specific GnRH receptors have been shown, but so far no GnRH-receptors have been isolated from the human testis. In this study testicular tissue from nine elderly men was incubated with either 3H-pregnenolone or 3H-progesterone and the steroid metabolic patterns were analyzed. In parallel incubations a GnRH-agonist was added to the incubate in concentrations of 10(-6) M or 10(-7) M. Furthermore, receptor studies were performed in tissue specimens from four of these untreated patients as well as in tissue specimens from five GnRH-agonist treated patients. No consistent effects were elicited by the addition of GnRH-agonist on the steroid metabolic patterns in vitro after three hours incubation. In the receptor studies the GnRH-agonist was bound to the testicular tissue, although the binding sites were of low affinity and high capacity, indicating a less specific kind of binding than classical receptor binding.