The duration of active social investigation by sexually mature male rats, following exposure to a novel conspecific, was investigated to assess the influence of former social experience. In Experiments 1 and 2, pretest social isolation of older males with extensive heterosexual experience and of younger males with limited heterosexual experience failed to affect their subsequent persistence in social investigation. Older and sexually experienced rats, however, engaged in significantly less investigatory behavior than did younger, sexually inexperienced males. Experiments 3, 4, and 5 demonstrated that this difference was associated with prior copulatory experience. A single copulatory series with either an intact female or a hormone-primed castrate female effected a significant and sustained decrease in social investigatory behavior. The results are interpreted as demonstrating a form of long-term memory for associations formed during initial copulatory experience.