Plasma triglyceride concentration and blood oxygen tension were measured in samples obtained by cordocentesis from 35 small- and 54 appropriate-for-gestational-age fetuses at 18 to 36 weeks' gestation. In the appropriate-for-gestational-age fetuses there was an exponential decrease in plasma triglycerides with gestation. Some small-for-gestational age fetuses were hypertriglyceridemic and the degree of this biochemical disturbance was significantly correlated with the degree of fetal hypoxemia.