McClintock found that female rats living in isolation or in groups synchronized their ovarian cycles, and she proposed a two-pheromone mechanism to explain synchrony: one pheromone shortens cycles and the other lengthens them. Subsequent research revealed that the preovulatory pheromone shortened cycles, whereas the ovulatory pheromone lengthened cycles. Schank and McClintock modeled this mechanism with computer simulation, assuming variability in sensitivity to pheromones during the ovarian cycle, and found that a coupled-oscillator mechanism can synchronize cycles, if pheromone sensitivity is highest around the time of ovulation. In this paper, we report the effects of pulses of ovulatory pheromone on the ovarian cycles of isolated female rats. Donor females were in the ovulatory phase of their cycle and recipient females were in olfactory isolation except during specified phases of their ovarian cycles. Recipient females showed significant shortening in ovarian cycles, with no significant variability in sensitivity to the ovulatory pheromone during the ovarian cycle. We discuss these conflicting results in terms of the experimental context of recipient females and the components and complexities of pheromone signals.