In recent years evidence has accumulated that hypothalamic hormones may influence behaviour directly, independently of their hypophysiotropic effects. Such a dual role has also been shown for several peptide hormones of pituitary and peripheral origin. The present synopsis is concerned with the effects of neuropeptides on spontaneous behaviour, acquired responses in certain psychological test situations, and drug-induced behavioural effects. A growing body of evidence suggests, that neuropeptides are involved in different behavioural processes. Some peptides selectively influence behaviours such as feeding, drinking, sexual responses etc. Other neuropeptides seem to influence behaviour by acting on processes which are a common integral part of the production of behaviour, namely the ability to receive environmental stimuli, to consolidate, retain and retrieve information. The insight into these mechanisms is important for the understanding of mental disturbances and in order to find specific therapy.