Sprague-Dawley rats received three dietary levels of essential fatty acids (EFA) during gestation and the suckling period and up to adult age by raising them on their respective diets for more than two generations. The relative difference in body weight was most pronounced between 13 and 23 days of age, after which it gradually diminished. Between 25 and 60 days of age, rats fed 0.07 cal% EFA had a significantly lower body weight than rats fed 0.75 cal% and the latter had a significantly lower body weight than those fed 3.0 cal%. The difference was slightly more Pronounced for females than for males.