It is planned to study the nature of the metabolites of testosterone that are formed in the limbic system and the role they play in mediating the actions of testosterone on this structure. The functions of the putative active metabolites, e.g. dihydrotestosterone and estrogens, will be studied for their effects on mechanisms related to neurosecretory phenomena and aggressive and sexual behavior. The approaches proposed include static and continuous flow incubations, enzyme inhibitors and animal models in which specific environmental and genetic influences have been identified. The relevance to the human of information derived from the experimental animals will be tested. The experiments proposed should provide information on the possibility of selective modification of specific androgen dependent brain functions through the use of steroid metabolites or by modifying steroid metabolism.