The paper describes and compares the influences of the antidepressants (imipramine, mianserin, citalopram), electroconvulsive shock, and the neuroleptics (haloperidol, chlorpromazine and spiperone) on the systems of second messengers related to adrenergic receptors in rat cerebral cortex, measured by generation of cyclic AMP and inositol phosphate (IP), and their influence on the effects of activation of protein kinase C (PKC) by its synthetic activator, phorbol ester (TPA). The effect of PKC-stimulation was expressed as a reduction of noradrenaline-stimulated IP accumulation and, on the other hand, as an enhancement of cyclic AMP response under stimulation with noradrenaline and isoproterenol. When administered chronically, the described antidepressants (unlike the neuroleptics) augmented IP accumulation or left it unchanged, but they reduced PKC's negative feedback with the alpha 1-adrenoceptor. PKC-induced potentiation of cyclic AMP's response to beta-adrenergic receptor stimulation was unchanged or enhanced, while the antidepressants reduced the generation of this second messenger. However, citalopram increased cyclic AMP generation and reduced PKC potentiation. Taking into account the role of PKC in adrenergic receptors cross-talk explains why, despite antagonization of alpha 1-adrenoceptors and induction of beta down-regulation by some antidepressants, enhancement of the process of noradrenergic neurotransmission can occur as a final effect of the action of these drugs. It was found that the action of antidepressants is largely related to the adrenergic system, even when their action on this system is not direct and is accomplished by their influence on another neurotransmitting system, e.g. the serotonergic system.