AbstractYoung female laboratory mice reared in the presence of an adult male mouse or male bedding containing a pheromone reach sexual maturity earlier than control females. A pheromone produced by grouped female mice leads to long, irregular estrous cycles or anestrus. The present study demonstrated that a female‐produced pheromone delays sexual maturation when females are grouped and that free social interaction and tactile contact among the grouped females are necessary for the production of this inhibitory pheromone. Both young and adult females caged in groups produced the inhibitory pheromone. This study provided additional support for the hypothesis that in female mice morphological and sexual development are under separate control mechanisms. Two pheromones may be active in reproductive processes of female mice: one exhibiting inhibitory effects and the other acceleratory effects.