Amino acid profiles and total amino-acid concentrations are established in nonfasting plasma of pregnant control, mildly diabetic and severely diabetic rats, and of their fetal and adult offspring. In pregnant rats at day 20 of gestation plasma amino acids can be regarded as normal in mildly diabetic mothers, but are significantly decreased in severely diabetic mothers. In fetuses of control rats, amino acid levels are twice as high as in the mother (fetomaternal ratio 2.0); in the fetuses of mildly diabetic mothers they are significantly lower than normal (fetomaternal ratio 1.3); in the fetuses of severely diabetic mothers they are also significantly lower than normal but with a normal fetomaternal ratio (fetomaternal ratio 2.0). In adult offspring of mildly diabetic mothers the concentration of almost all amino acids as well as that of total amino acid pool is significantly lower than in the controls; in the offspring of severely diabetic mothers they can be regarded as normal. No specific amino acid or group of amino acids can be held responsible for any of these changes, since all differences with control values display an overall effect, involving all or almost all amino acids.