Correlational research has linked mate availability to human sexual behavior, whereby unrestricted sociosexuality seems to be most common under conditions of female abundance. In this study, 71 heterosexual men were randomly assigned to one of two mate availability priming conditions, mate scarcity or mate abundance, and subsequently completed measures of sociosexuality as well as infidelity intentions. Results indicated that men in the mate abundance condition reported stronger sociosexual attitudes and desires, and among those currently in relationships, stronger infidelity intentions. These findings were contrasted with those from a separate sample of 66 heterosexual undergraduate women. Mate scarcity had no effects on women's sociosexuality or infidelity intentions. Findings suggest that when mates are scarce, men will adopt a sociosexual orientation aimed at maintaining a single partner.