The plant compound, 6-methoxy-2-benzoxazolinone (6-MBOA), is found in the meristematic tissue of young, vegetatively growing grasses, and its ingestion stimulates the reproductive system of rodents in both short and long photoperiods. The present study demonstrates the existence of a novel mechanism whereby the presence of 6-MBOA in the diet of pregnant prairie voles (Microtus ochrogaster) enhances gonadal development in their male offspring. Female voles were fed specially milled food in which 6-MBOA was present (50 micrograms of 6-MBOA/g food) or absent (0 microgram of 6-MBOA/g food) prior to the birth of their young; all of these dams received a diet that lacked 6-MBOA/g after the pups were born. Other females were fed food without 6-MBOA throughout pregnancy, but received one of the two diets during lactation. The pups from all experimental groups were weaned at 3 weeks of age and fed thereafter one of the two diets for 3 additional weeks. Prenatal exposure to 6-MBOA enhanced male reproductive development. Maternal ingestion of 6-MBOA during lactation or postweaning intake of 6-MBOA by the young did not influence reproductive development of males. This mechanism may be involved in the rapid rate of sexual maturation observed prior to peak population densities of microtine rodents.