Stress during pregnancy, or prenatal stress, is known to alter offspring behavior, morphology and physiology. We found that a heat, light and restraint stressor applied during the third trimester of pregnancy: 1) decreased the weight gain of adult female rats during pregnancy; 2) reduced the weight of pups, as well as the anogenital distance of male offspring, at birth; and 3) increased the number of ultrasonic vocalizations emitted by pups during isolation in a novel environment on Postnatal Day 14. These results closely approximate those we previously observed after peripheral administration of corticotropin-releasing factor to pregnant females during the third trimester. Together, the studies strongly suggest a role for corticotropin-releasing factor and/or other hormones of the hypothalamic-pituitary-adrenal system in mediating some of the effects of gestational stress.