The concentration of taurine in fetal blood and in mother's milk is very high. In the present study, in order to elucidate the nutritional role of taurine during fetal and neonatal age we investigated the urinary taurine excretion and the blood taurine concentration change in premature babies. 1. The blood taurine concentration of infants on the first postnatal day decreased along with gestation between 7-10 gestational months. On the other hand, there was no difference in the concentrations of blood total amino acids in infants on the first postnatal day in 7-10 gestational months. 2. The blood taurine concentration of infants decreased remarkably during one week after birth. This tendency to decrease was more prominent in premature infants--those at 8 to 10 gestational months. 3. The urinary excretion of taurine and total amino acids of infants remarkably decreased along with gestation between 7-10 gestational months. This tendency to decrease was the most prominent in infants between 7 and 8 gestational months.