The effect of i. v. administration of angiotensin II, substance P, DSIP, B-endorphin and bradykinin on the behaviour and the somato-vegetative responses to electrical stimulation of negative and positive emotiogenic regions of the hypothalamus, were studied. Angiotensin II, substance P and DSIP suppressed the avoidance and self-stimulation responses and inhibited cardiovascular responses. Bradykinin, renin and B-endorphin increased the latency of avoidance responses, enhanced and prolonged the somato-vegetative responses to electrical stimulation of negative emotiogenic regions of the hypothalamus. Possible mechanisms of the peptides physiological activity are discussed.