Abstract Ten adult male Beetal goats were used for the study to elucidate the modulation of gonadotrophin, prolactin and testosterone secretion by endogenous opioid peptides. An indwelling catheter was placed in the jugular vein of each buck 20 h before the onset of the experiment. Bucks were divided randomly into two groups: Group I ( n = 5) received naloxone at a dose rate of 1 mg/kg body weight (BW) and Group II ( n = 5) received naloxone at a dose rate of 2 mg/kg BW intravenous. Blood samplings were done from 2 h before treatment until 2 h after treatment at 15 min intervals. Blood samples were quantified for plasma LH, FSH and prolactin concentration using a heterologous double antibody radioimmunoassay (RIA) and testosterone concentration was quantified by coat-a-count RIA kit. The mean plasma LH levels during pretreatment phase were 0.41 ± 0.03 ng/ml in Group I and 0.44 ± 0.02 ng/ml in Group II which significantly ( p < 0.05) increased to 0.91 ± 0.05 ng/ml in Group I and 1.53 ± 0.07 ng/ml in Group II. The mean plasma FSH levels did not show a difference in pre- and post-treatment animals in both groups. A significant ( p < 0.05) increase in plasma testosterone concentration was observed in both groups after naloxone treatment, whereas, a decrease ( p < 0.05) was observed in plasma prolactin levels after naloxone treatment. Thus, it can be concluded that endogenous opioids do play an important role in modulating plasma LH, prolactin and testosterone concentrations in male goats.