'Memory' for a juvenile conspecific in male rats can be measured by variation in duration of investigation times when the same juvenile is presented at different intervals. Typically, exposure of an adult male rat to a juvenile results in transient investigatory activity that rapidly declines with repeated exposures at short interexposure intervals (30 min). Longer interexposure intervals (120 min) result in re-investigation with durations similar or greater than the original investigation. Arginine vasopressin (AVP) injected into adult male rats intracerebroventricularly in doses of 0.5-2.0 ng immediately after investigation of the juvenile decreased social investigation of the same juvenile at the long (120 min) interexposure interval. This decrease in investigatory time was similar to that observed after a 30-min interexposure interval in untreated animals. These results support the hypothesis that increasing the availability of AVP in the central nervous system can improve the consolidation of olfactory information and improve conspecific recognition in rats.