The relationship between behavioral polymorphism and the variation for the function of the hypothalamic-pituitary-adrenocortical axis (HPAA) was studied in the meat-and-wool (n = 447) and Altaian fine-fleece (n = 45) sheep breeds under production farm conditions. The behavior studied included negatively associated reactions: feeding reactions and defensive reactions in relation to human. In sheep, the intrapopulation variation for the stress level of corticosteroids depended on the effect of behavior, the type of stimulus, and the interaction between these two factors and correlated with the behavior phenotype (r varied from -0.551 to -0.226). In the stress responses to either 24-h starvation or lamb weaning, hormonal reactions were similar in wild-type sheep that have clearly marked defensive reactions and in the sheep of the domestic phenotype that was contrasted to the wild type. In the stress responses to isolation from the herd, transportation, and competition for food, hormonal reactions were stronger in the wild type than in the domestic phenotype; alternatively, in the stress response to being kept in cages in pairs, hormonal reaction was stronger in the domestic phenotype than in the wild type. In the sheep that were placed in cages, a single playing of tape-recorded anxiety signals caused the motivational or emotional stress that was characterized by an unusually long latent period of the progressive HPAA reaction and its subsequent chronic course (up to 9 days). Animals of contrasted behavioral phenotypes differed in the course of the HPAA reaction. Heritable behavioral polymorphism and interaction between behavior and the type of stimulus are the regulation factors in the expression and variability of stimulus-specific reactions of HPAA. Behavior can serve as the genetic marker for individual features of HPAA functioning in the stress response of sheep.