The value of clinical parameters and umbilical arterial blood pH as indicator of prenatal hypoxia is disputed. In a prospective study of 86 vaginally delivered full-term infants, cardiotocographic (CTG) findings obtained 0-30 min and 30-60 min before birth were compared to pH values, O2 and CO2 partial pressures and glucose difference in umbilical arterial and venous blood. CTG findings were expressed as a score, higher values indicating fetal hypoxia. The venous but not the arterial blood pH was significantly related to the later (0-30 min) CTG score. The arterio-venous glucose difference was significantly related to both CTG scores. There was a significant statistical relationship between glucose difference and venous but not arterial blood pH. The later CTG score (0-30 min) also correlated significantly with O2 and CO2 partial pressures and base excess in the umbilical vein of all vaginally born infants. If CTG is accepted as an objective indicator of fetal hypoxia before birth, the arterio-venous glucose difference, and in the investigated range of pH-values, umbilical venous blood pH are more suitable than the arterial blood pH to ascertain the peripartal situation of the newborn.