Results of these experiments indicate that females given at least 24 hours of cohabitation with a male develop a social preference for the familiar partner versus a stranger. Mating is not essential for the development of partner preferences, but clearly facilitates the onset of preferences. Females given six hours of cohabitation showed partner preferences only if they mated with the partner during cohabitation (Experiment 2) or if they received oxytocin (Experiment 3). Females that continued to mate during preference tests (Experiment 2, n = 4) mated exclusively with the partner. Oxytocin infusions, even in the absence of mating or estrogen priming, facilitated the development of partner preferences.