The effects of drugs which interfere with alpha-adrenergic and dopaminergic mechanisms, involved in GH and PRL secretion, have been analyzed in urethane anesthetized rats. Clonidine induced a dose-dependent release of GH (0.0032--0.1 mg/kg i.v.) as well as of PRL (0.032--1.0 mg/kg i.v.). The lowest dose of clonidine, when given into the third ventricle, provoked a very pronounced release of GH. Phentolamine, given intravenously, inhibited the clonidine-induced GH release in a dose-dependnet manner. L-Dopa administered intravenously and apomorphine administered intravenously or intraventricularly did not affect basal secretion of GH bu- produced a dose-dependnet inhibition of clonidine-induced GH release. Pimozide did not change basal GH secretion. Furthermore pimozide did not attenuate the inhibition of clonidine-induced GH secretion seen after apomorphine administration, however, it completely reversed apomorphine-induced PRL inhibition. These findings demonstrate that an alpha-adrenoceptor-mediated stimulatory mechanism is involved in GH and PRL secretion. An inhibitory dopaminergic mechanism is confirmed for PRL secretion and suggested for GH secretion.