Previous studies designed to elucidate behavioral-endocrine mechanisms of possible relevance to regulation of population growth have demonstrated that socially-derived stimuli associated with increasing density or presence of adult animals are capable of inhibiting testis development in prepubertal mice. However, components of the stimulus melange associated with social interaction which may contribute to testicular inhibition have not been elaborated. Moreover, although social experience is a factor influencing the stimulus quality of adult males, the possible relevance of alterations in stimulus quality to reproductive behavior have been afforded little attention. Studies therefore are proposed which would: (1) examine the role of olfactory stimuli in inhibition of testis development, (2) determine neural-endocrine mechanisms through which exteroceptive, socially-derived stimuli may modify testis function, and (3) determine effects of intermale aggression and social rank on stimulus qualities relevant to reproductive performance. Methods utilized to test pertinent hypotheses will incorporate previously developed behavioral models, including adult intermale aggression and cohabitation of juveniles with adults. Results of these studies should help to determine the influence of specific sensory modalities or stimuli affected by and associated with the social environment upon prepubertal development and adult reproductive performance in males.