It is well established that the behavior of different mammalians, including rodents, may undergo profound changes in the presence of individuals of other species. Therefore, the aim of this study was to verify if the presence of pheromones from male mice could influence the reproductive parameters of female rats. Twenty Swiss (SW) male mice and 16 Long Evans (LE) female Rats were housed in separate rooms, with communication in the ceiling in its entire length. A continuous flow of air was planned to pass through the room of the mice before the room of the rats and finally be exchanged with the external environment. During 45 days, vaginal smears were collected. Relative weights of reproductive organs, estradiol, progesterone, and dehydroepi...