The roles of ionotropic glutamate receptors in mammalian reproduction are unknown. We therefore generated mice lacking a major subtype of (S)--amino-3-hydroxy-5-methyl-isoxazolepropionic acid (AMPA) receptors or all N-methyl-D-aspartate (NMDA) receptors in GnRH (GnRH) neurons and other mainly limbic system neurons, primarily in hypothalamic and septal areas. Male mice without NMDA receptors in these neurons were not impaired in breeding and exhibited similar GnRH secretion as control littermates. However, male mice lacking GluR-B containing AMPA receptors in these neurons were poor breeders and severely impaired in reproductive behaviors such as aggression and mounting. Testis and sperm morphology, testis weight, and serum testosterone levels, as well as GnRH secretion, were unchanged. Contact with female cage bedding failed to elicit male sexual behavior in these mice unlike in control male littermates. Their female counterparts had unchanged ovarian morphology, bred successfully, and had normal litter sizes but exhibited pronounced impairments in maternal behaviors such as pup retrieval and maternal aggression. Our results suggest that NMDA receptors and GluR-B containing AMPA receptors are not essential for fertility, but that GluR-B containing AMPA receptors are essential for male and female reproduction-related behaviors, perhaps by mediating responses to pheromones or odorants.