The copulatory performance of male rats (Sprague-Dawley) was quantified, and the factor analytic technique applied to the data. Since factor analysis assesses common variance, subject selection was organized so as to maximize behavioral heterogeniety. Three factors were retained in the statistical analysis. The variables in two factors, Copulatory Efficiency and Initiation, were similar to those contained in the two factors posited by Beach (1956). The third factor was Intromission Count; it contained 2 variables, intromission frequency (IF) and post-ejaculatory interval (PEI). Unlike the variables in the other two factors, however, IF and PEI were not significantly correlated in a simple correlation analysis. The absence of a correlation suggested that the Intromission Count factor contained a suppressor variable. Although the identity of the hypothesized suppressor variable is not known, others have shown that IF and PEI are systematically related to adrenal hormones, the female's behavior and to dominance position. Therefore, the present results suggest that the Intromission Count factor may bear a significant relationship to a broad range of social behaviors, in addition to copulation. In a second experiment an attempt was made to independently manipulate the Initiation and Copulatory Efficiency factors by making elecrolytic lesions of either the median or dorsal raphe nuclei. While there were no significant differences among the groups on measures of copulatory or non-copulatory social behav- iors, a pattern of differences in those behaviors emerged which suggested that the serotonergic system may interact with the olfactory system to influence the two copulation factors. / Master of Science