Using radioimmuno-and ribonuclease protection assays, we examined the effects of gonadotropin-releasing hormone and its analogs on the growth hormone mRNA level and growth hormone secretion in common carp (Cyprinus carpio) pituitary fragments with static incubation. After a 24h treatment, sGnRH (wTrp7,Leu8x-LHRH) and sGnRH-A (wDArg6, Pro9x-LHRH) (0.1nM-1mM) elevated the GH mRNA level and stimulated the GH secretion in a dose-dependent manner, with a higher potency for sGnRH-A. In a time-course experiment, the function of sGnRH and sGnRH-A (10nM) on GH secretion was observed after 6h incubation, while no action on the GH mRNA level were noted until 12h after treatment. Comparing mammalian GnRH, avian GnRH and piscine GnRH, sGnRH and sGnRH-A showed the highest potency in increasing GH mRNA level and GH-release, followed by cGnRH-II (wHis5,Tyr8x-LHRH), and finally LHRH and LHRH-A(wD-Trp6, Pro9x-LHRH). These findings, taken together, suggest that GnRH not only can influence GH release, but also play a role in the regulation of GH synthesis.