Female rats were fed purified rations containing 20% fat during gestation and lactation. The fat content was butter oil, an equal mixture of butter oil and lard, or safflower oil. Each litter size was reduced (at random) to 2 male and 2 female pups 1 day postpartum, and these offspring were feed a commercial ration after weaning and until they were 20 weeks of age. When dams were fed safflower oil, fewer of them produced litters after mating, and their behavior during lactation was less than optimal. Litter size and birth weights were similar in all dams producing litters. The type of fat fed to the dam in the perinatal period did not influence the growth, development, and spontaneous activity of the offspring. However, the offspring from the dams fed safflower oil exhibited poorer learning performance in a T-maze and sometimes had a longer time of inactivity following auditory stimulation than did the offspring from dams fed the other types of fats.