To examine the role of GABA(A) receptor mediating systems in the control of gonadotropin-releasing hormone (GnRH) release from the ventromedial-infundibular region (VEN/NI) in ewes during luteal phase, the extracellular concentrations of GnRH, beta-endorphin, noradrenaline (NE), dopamine (DA), and their metabolites: MHPG and DOPAC were quantified by local stimulation or blockade of GABA(A) receptors with muscimol or bicuculline, respectively. Stimulation of GABA(A) receptors in the VEN/NI did not affect GnRH, beta-endorphin release or catecholaminergic system activity. Blockade of GABA(A) receptors decreased beta-endorphinergic and dopaminergic activity, and lowered the extracellular concentration of MHPG. It did not affect GnRH release or luteinizing hormone (LH) secretion. It is suggested that progesterone-induced GABAergic activity during the luteal phase may desensitize GABA(A) receptors to muscimol. Lack of changes in GnRH/LH secretion with concomitant depressed beta-endorphinergic activity corroborated the conclusion that beta-endorphin does not inhibit GnRH release from the VEN/NI during the luteal phase. The physiological significance of changes in the catecholaminergic system activity under GABA(A) receptor blockade in the control of GnRH secretion awaits to be established.