Because infant rats learn about odors that elicit suckling, and because certain chemosensory cues that help elicit mating behavior in adults are similar to those that elicit suckling, an experiment was undertaken to assess the influence of suckling-associated odors experienced during infancy on adult sexual behavior. Rat pups lived with and suckled dams whose nipple and vaginal odors were altered with citral, a lemon scent. The rats were weaned and never exposed again, until testing, to citral or females. At about 100 days of age, the males were paired in mating tests with a normal sexually receptive female or with a sexually receptive female that had been treated perivaginally with citral immediately before testing. The males ejaculated readily when paired with citral-treated females but were slow to achieve ejaculation when paired with normal females. These findings implicate an infantile experience as a determinant of adult sexual behavior in a mammal.