Growth rate of the offspring of female rats stressed by the presence of a cat at the 10th or the 19th gestational day was lower than that of controls whereas footshocks administered at the same periods did not significantly influence growth rate of the young. Whatever the nature of the stress and the time when it was administered to the mother, the death rate of the young rats was much greater than that in controls. When adult, the offspring of stressed mothers exhibited learning and memory impairments in a delayed alternation task as well as in passive avoidance conditioning. Alteration of these cognitive functions is interpreted in terms of subtle dysfunctions in the development of the nervous system through modifications of the hormonal components of the mothers, particularly eventual alterations of the nervous system biochemistry of the offspring.