Factors which regulate intraspecific and interspecific social preferences are being investigated. In the period covered by this report it has been determined or confirmed that both male and female hamsters display strong social preferences for conspecifics over heterospecifics. In neither males nor females is sexual experience required for the intraspecific preference behavior to be exhibited. The preference behavior of male hamsters is in part based on species- and sex-specific olfactory cues produced by perivaginal glands. Intraspecific sexual preferences of female hamsters are in part based on factors relating to testosterone levels of conspecific males (e.g. dominance, level of scent-marking, having intact gonads, having a normal size scent gland.)