The effects of cholinergic modulation by hexamethonium (HEX), tetraethylammonium (TEA), pirenzepine (PIR) and neostigmine on growth hormone (GH) secretion induced by galanin (GAL) were investigated in awake, freely moving male rats. Intracerebroventricular (i.c.v.) injection of GAL (0.6 nmol) caused a marked increase in plasma GH levels. Pretreatment with HEX (3 or 15 mg/kg BW), TEA (15 mg/kg BW) or PIR (0.5 mg/kg BW) significantly reduced the GAL-induced GH secretion. Pretreatment of animals with neostigmine (0.05 mg/kg BW) or with a specific antisomatostatin antiserum (10 microliters of 1:10 diluted with saline, i.c.v.) reversed the inhibition of GAL-induced GH secretion by HEX. These findings suggest that both nicotinic and muscarinic cholinergic mechanisms interact with the galanin-induced GH secretion by modulating hypothalamic somatostatin release.