The pH, pCOg and standard bicarbonate of the amniotic fluid has been determined in 26 cases of late pregnancy. The material was divided into two groups, one consisting of pregnancies considered normal and the other of pathological pregnancies including diabetes mellitus, toxemia, Rh-immunization and post-maturity. In the pathological group the pH and the standard bicarbonate of the amniotic fluid was significantly lower and the pCO2 higher as compared to the control group. The pCO2 and the acid-base status of umbilical cord blood was compared to that of the amniotic fluid in four cases of cesarean section. The results have been discussed in the light of intrauterine conditions of the fetus and it is suggested that studies of the amniotic fluid could give valuable information about fetal asphyxia.