In experiments with cats, air-assisted microinjections of mexidol and melatonin had a direct effect on 71-81% Purkinje cells inducing the inhibitory response 4.2-6.3 times more often than exiting. In case of concurrent action of MK-801 (a specific noncompetitive NMDA-receptor antagonist) the mexidol effect on the spontaneous activity was suppressed fully or abated significantly in 88% Purkinje cells. Lusindol (a specific melatonin MT2- and MT2-receptor antagonist) and GABA-negative bicuculline prevented the inhibiting effect of melatonin fully or abated significantly the spontaneous activity of 86% and 71% Purkinje cells, respectively. This means that melatonin-produced inhibition recruits both melatonin MT1- and MT2-receptors, and also the GABA-ergic component (stimulation of GABAA-receptors). Investigation of rat's cerebellum slices with prolonged survival showed that 5 mM of mexidol inhibited reliably Purkinje cells population responses by 93 +/- 4%; the presence of MK-801 (100 microMM) weakened this effect by 82 +/- 3%. Consequently, mexidol is capable to inhibit strongly the parallel fibers--Purkinje cells synaptic transmission in the rat's cerebellum, whereas MK- 801 abates this effect appreciably.