While Freudian theory emphasizes the importance of infantile experience upon adult behavior, "Much if not most of the presently available evidence bearing upon this problem is equivocal and of undetermined reliability" (3, pp. 256-7). Although some effects of early experience on later behavior have been adequately demonstrated (cf. 3, 7, 8), conflicting results have been reported on this relationship in the area, of animal sexual behavior. Rearing rats in isolation has been shown to have no effects on the pattern of the copulatory response either in males (1) or females (9). Beach (1) reports that a greater percentage of males raised in isolation copulated than did males raised in cohabitation or segregation. Similarly, a group of males with no early sex experience had more copulators who ejaculated on adult sex tests than a group of males with early sex experience (6). However, Jenkins, using frequency of grid-crossings as her measure, found that the sex drive in males segregated before puberty was subnormal, and homosexual tendencies developed (5). A recent study by Valenstein, Riss, and Young (10) indicated that male guinea pigs reared in cohabitation showed a significantly greater amount of sexual behavior than males reared in isolation. Haywood (4) has apparently demonstrated that early avoidance training significantly inhibits the adult sexual behavior of the male rat; however, the generality of this conclusion will be examined at length in a later section of this paper. The present study was designed to answer the following questions: (a) Does shocking a young male rat for approaching a receptive female inhibit normal sexual responses in adulthood? (b) Does rearing male rats in isolation or part-time cohabitation have a differential effect on their adult sexual performance when tested with a receptive female? (e) Is there an interaction between early avoidance training and type of subsequent rearing condition on adult sex behavior? Accordingly, a 2 X 2 design was utilized in which 12 male hooded rats were randomly assigned to an early shock condition and 8 rats to a control no-shock condition. Each of these groups was then subdivided into two groups, either reared in isolation or cohabitation. (PsycINFO Database Record (c) 2006 APA, all rights reserved)