AbstractIn human pregnancy, maternal and umbilical blood of the 22nd and 40th weeks of pregnancy and at parturition were submitted to the analysis of total free amino acids (FAA) by the amino acids analyzer. The neonatal blood was also submitted until the 9th day after birth. The content of FAA in the serum from the umbilical vein was higher than that from the maternal blood, and it decreased at the parturition term.However, the content of taurine kept a much higher level than the other amino acids until term, and then it decreased to the normal level on the 9th day after birth. In pregnant rats on the 17th, 18th and 19th days of gestation, the content of FAA in the serum from the umbilical vein and fetal artery was twice as high as that of the maternal serum. In amniotic fluid, FAA content was increased on the 20th day. On the contrary, the content of taurine in fetal blood was at the highest level on the 18th day, after which it decreased until the 20th day. The level of taurine in the carotid artery decreased on the 20th day. In the amniotic fluid, it was almost constant. When the pregnant rat was starved, the level of FAA was increased in both umbilical and fetal blood, but it was almost constant in the amniotic fluid. Taurine content was increased in maternal and fetal blood by starvation, and increased also by irradiation. When the degree of starvation proceeded, taurine content increased correspondingly in the fetal blood.