The influence of hydrocortisone acetate treatment (4 mg/100 g body weight i.m. and daily injected) was studied in pregnant rats and their litters. The parameters controlled were: food intake, body weight and body nitrogen, and liver enzimatic activity of PEPCK, in the mothers and number of foetus, weight, body nitrogen content and liver PEPCK activity in the litter. The hormonal treatment induces a significant reduction of food intake and weight of the mothers. In the same way the total body nitrogen content, is reduced but not its concentration (body nitrogen content/g body weight). Likewise, cortisone injection reduces the number of newborns, and, significantly, the individual weight of the same. At the 21st gestation day, the nitrogen content of the litter, given by g of weight, is also significantly reduced. Liver activity of PEPCK was significantly increased in the pregnant rat in all days under study and was not detected in the foetus in the 21st day.