Experimental data of physiological activity of synthetic analogs of three novel neuropeptides isolated from the bovine brain are presented. The characteristics of the influence of the peptides on various forms of aggressivity of rats--intermale, predatory, and defense--with central and peripheral administration, are demonstrated. The influence of the peptides on other types of behavior--the consumption of food and water, fear, locomotor activity--associated with the formation of aggression is demonstrated. The modulatory effects of the peptides on the responses of identified neurons of molluscs to neuromediators, serotonin, dopamine, and glutamate, which participate in the neurochemical support of aggressive behavior of rats, are documented.