Postnatal development of liver tyrosine aminotransferase and glucose-6-phosphatase, expressed as activity per gram of liver, occurred as rapidly in pups from pregnant rats fed throughout gestation a diet containing only 4% of casein as in pups from those fed the control diet containing 18% of casein supplemented with 0.3% of L-methionine. Total enzyme activity per liver was lower in pups from protein-restricted dams due to their smaller liver size. Dams fed the 4% casein diet during pregnancy gained much less weight than those fed the control diet and produced pups that weighed significantly less than control pups. Reproductive performance of a few dams fed 6% casein diets with or without amino acid supplements during gestation was comparable to that of dams fed the control diet. Litter size was not significantly reduced by the low-protein intake.