Both men and women find female voices more attractive at higher fertility times in the menstrual cycle, suggesting the voice is a cue to fertility and/or hormonal status. Preference for fertile females' voices provides males with an obvious reproduction advantage, however the advantage for female listeners is less clear. One possibility is that attention to the fertility status of potential rivals may enable women to enhance their own reproductive strategies through intrasexual competition. If so, the response to having high fertility voices should include hormonal changes that promote competitive behavior. Furthermore, attention and response to such cues should vary as a function of the observer's own fertility, which influences her ability to compete for mates. The current study monitored variation in cortisol and testosterone levels in response to evaluating the attractiveness of voices of other women. All 33 participants completed this task once during ovulation then again during the luteal phase. The voice stimuli were recorded from naturally cycling women at both high and low fertility, and from women using hormonal birth control. We found that listeners rated high fertility voices as more attractive compared to low fertility, with the effect being stronger when listeners were ovulating. Testosterone was elevated following voice ratings suggesting threat detection or the anticipation of competition, but no stress response was found.