Obese female Sprague Dawley Rats were randomly assigned, on a weight basis, to one of three dietary treatments: ad libitum, 30% caloric restriction, and 50% caloric restriction. All other nutrients were fed at levels to meet dietary requirements. Each treatment group was further divided into pregnant and nonpregnant subgroups. The experimental diets were started on Day 4 of gestation for pregnant groups. Rats were sacrificed on Day 20 of gestation and fetuses were taken by Caesarean section. Maternal and fetal body composition, and the maternal serum protein concentration were examined. Weight changes for pregnant rats were +127 gms in the ad lib fed group, +83 gms in the 30% restricted group, and +51 gms in the 50% restricted group. Weight changes for the nonpregnant rats after 20 days of dietary treatment were +22 gms, -10 gms, and -40 gms in the ad lib fed, 30%, and 50% restricted groups respectively. The percentage of maternal carcass protein was affected by the 50% caloric restriction imposed on all animals. Animals on the 30% and 50% caloric restricted diet showed a decrease in total body fat of 5% and 12% respectively, as compared to the ad lib fed controls regardless of pregnancy state. The maternal liver weight increase during pregnancy was less in 30% and 50% caloric restricted animals. Serum protein levels decreased in pregnant animals as caloric restriction increased. Fetal body weight, brain weight, and body composition did not differ between treatment groups. The fetal compartment was not affected by maternal caloric restriction up to 50% while providing all other nutrients adequately. Maternal stores were affected at both levels of 30% and 50% caloric restriction. These results indicate that excess fat stores can be mobilized to support fetal growth in obese pregnant rats under caloric restriction, when other nutrients are provided in adequate amounts. / M.S.