The aim of the present work was to explain the mechanism of the stimulating effect of adrenaline (A) on acetylcholine (ACh) synthesis. This action is exerted most probably through the beta- adrenergic receptors, since propranolol and oxprenolol inhibit the stimulating effect of adrenaline on acetylcholine synthesis in the rat cerebral cortex in vitro. Dihydroergotamine does not show such effect. Practolol and phentolamine decrease the spontaneous synthesis of ACh in concentration several times lower than that inhibiting the ACh synthesis stimulated by adrenaline. It is suggested that adrenaline-induced stimulation of ACh synthesis in the rat cerebral cortex is not due to cyclic AMP, because noradrenaline (NA) does not increase ACh synthesis either in vivo or in vitro, although it activates the adenyl cyclase. NA on the other hand activates ACh synthesis in the calcium-free medium, which inhibits activating effect of NA on adenyl cyclase. Moreover it was found that cyclic AMP depresses ACh synthesis in the rat cerebral cortex in vitro.