The roles of hypothalamic neuropeptides and their receptors were investigated during sexual maturation in the chicken. Using osmotic pumps implanted subcutaneously, GnIH was delivered 'in vivo' to immature roosters to prevent sexual maturation. No significant effect of GnIH was observed, and although the pumps were well tolerated, it appeared that the implantation site was inadequate. A novel antibody specific to cGnRH-R-III was developed and validated. Using this antibody and one directed against cGnIH-R, changes in cGnRH-R-III and cGnIH-R protein concentrations in pituitary glands of chickens during a reproductive cycle were determined. Western blot analyses show that cGnRH-R-III protein levels are significantly greater in sexually mature birds. Due to lack of specificity, consistent results could not be obtained for cGnIH-R. Finally, the effect of oestradiol, progesterone or a combination of the two on cGnRH-R-III and cGnIH-R mRNA levels in the pituitary gland were determined using real-time PCR. All three steroid treatments decreased both cGnRH-R-III and cGnIH-R mRNA.