By studying the influence of the arginine pyroglutamate on the CNS its variations were evidenced which are clearly identifiable through the analysis of the interaction with molecules having either a depressive or excitatory action. In the case of pentobarbital the antagonistic effect of the compound on the general anaesthesia is very intense and is equally present even when medazepam and flurazepam are associated. Equally obvious is the antagonism with barbiturate in the case of spontaneous motility but much less so with the two benzodiazepines. As far as the specialized behaviour is concerned, arginine pyroglutamate does not alter the sound discrimination capacity (responses in Sdelta punished) at fixed intervals (F.I.) nor does it influence the learning of a sound discrimination (responses in Sdelta punished) at varied intervals (V.I.). The process of learning is instead moderately accelerated in the case of a temporal discrimination and of a conditioned avoidance response (CAR) in the shuttle-box. No effect was found when the same amino acids were introduced alone or in random association. The hypothesis is proposed that the phenomena described depend on the different pharmacokinetics of arginine pyroglutamate that ensures brain concentrations sufficient to block the activity of depressive compounds but is not capable of influencing in a significant way the spontaneous and specialized behaviour of normal animals.