The functions of two classes of pheromone receptors have been identified by researchers, who have also found pheromones crucial to triggering the mating process in mice. "Interestingly, the pheromone that tells other mice that 'I am female,' or the one that tells others, 'I am ovulating,' do not do much on their own," says the investigator who led the study. "But when the two are presented together, the male mice showed great interest in courting and mating with the female."