It is well known that GHRH-induced GH secretion decreases after orchidectomy. To verify if testicular factors other than testosterone are involved in this effect, the GHRH-induced GH secretion and testosterone plasma levels were compared in adult male rats that were either intact, treated with ethylene dimethane sulphonate (EDS) (a specific toxin for Leydig cells), orchidectomized or testosterone-treated orchidectomized. We found that testosterone plasma levels and ventral prostate weight decreased to a similar extent in orchidectomized and EDS-treated males. GHRH-induced GH secretion only decreased in orchidectomized males. We conclude that testicular factors, other than androgens, increase GHRH-induced GH secretion.