The goal of this project is to specify the role of endocrine factors in determining submissiveness--the readiness of an individual to surrender following attack by an opponent. Two kinds of relationships are studied here, both focusing on the pituitary-adrenocortical hormones. The first relationship is the role of the individual's hormonal state prior to entering a competitive situation, the baseline hormonal state, in determining submissive responses. The second relationship is the role of the pituitary-adrenal responses to defeat in mediating the effects of that experience on subsequent submissive reactions. Two approaches are used in this project. In studying the first relationship, the animals are subjected to a range of hormonal manipulations prior to exposing them to aggressive opponents. In studying the second relationship, the individual's hormonal responses to defeat are altered by hormonal manipulations made immediately following an initial defeat and, then, the individual's subsequent submissive reactions are studied. This project will serve to increase our understanding of the way in which endocrine factors determine competitive characteristics.