Muricidal and non-muricidal Wistar rats were studied regarding the changes of the body weight, the volume of the liquid intake, the sensitivity threshold to electrical shock, horizontal and vertical locomotor activity during 40-days period of 20% ethanol consumption. The transition to the situation of "choice" (water and/or ethanol) was accompanied by a division of the animals into two groups: "water preferring" and "ethanol-preferring" rats. The angiotensin-converting enzyme and enkephalin-forming carboxypeptidase H activity in different brain regions, hypophysis and peripheral tissues, were defined. The results allow one to conclude that neurochemical mechanisms underlying aggressive behavior (muricidity) and alcohol addiction have originally distinct nature.