The study was designed to test the efficacy of a commercially available vaccine, Vaxstrate(R) (Arthur Webster Pty Ltd, Castle Hill, N.S.W.), to immunise adult male goats against GnRH. The general hypothesis tested was that immunisation of goats against GnRH using Vaxstrate(R) would suppress gonadotrophin secretion, steroidogenesis and gametogenesis in the testis, production of male odour and agonistic behaviour between males. We also compared intervals of 2 and 4 weeks between primary and booster immunisations and monitored recovery from immunisation for approximately 1 year.Twenty bucks of feral origin obtained from a commercial feedlotter were allocated to one of four treatment groups (n = 5): entire control (intact non-immunised bucks); Vaxstrate 2 (immunised with 1 mi of Vaxstrate(R) on Days 0 and 14); Vaxstrate 4 (immunised with 1 mi of Vaxstrate(R) on Days 0 and 28); and castrate control (surgical castration on Day 0). The level of immunity against GnRH was significantly elevated (P <0.01) 14 days following the booster immunisation compared with pre-treatment levels in both Vaxstrate 2 and Vaxstrate 4 treatments. Immunisation prevented the seasonal increase in LH and testosterone concentration seen in entire bucks, and resulted in lower concentrations of these hormones and FSH in vaccinated bucks from Day 28 (P <0.001). Scrotal circumference of immunised bucks was smaller than entire bucks from Day 56(P <0.05). Bucks in the Vaxstrate 2 and Vaxtrate 4 treatments had lower(P <0.01) odour scores than entire controls from Day 42 and 56 respectively. Numbers of spermatozoa ml(-1) were lower in immunised than entire bucks at Days 175 and 329 (P <0.05 and P <0.01 respectively). Agonist confrontations recorded at Day 64 in vaccinated bucks appeared to be intermediate between that of surgically castrate animals and entire bucks.The results have shown immunisation against GnRH in goats is effective in suppressing the increase in testes size, male odour and agonistic behaviour that is associated with the seasonal breeding season. Immunisation against GnRH was successful in all goats and in 90% of goats the testes remained small for more than a year following primary immunisation. In this experiment, a 2 week interval was as effective as a 4 week interval between primary and booster immunisations.