A quantitative comparison was made of fetal heart-rate (FHR) traces obtained shortly before delivery, and of umbilical artery blood gas values, in 49 women delivered by caesarean section for reasons other than fetal compromise and in 23 women delivered by section for antenatal fetal compromise judged from visual inspection of conventional FHR recordings. The FHR traces in the compromised group of fetuses were abnormal, with low variability and a high incidence of decelerations, but there was no significant difference from the normal group in metabolic acidaemia, as judged by the base excess of umbilical artery blood. The compromised group consisted almost exclusively of infants small-for-gestational age. These results suggest that the FHR pattern of the compromised fetuses is not the direct result of intrauterine asphyxia but of some other factor associated with growth retardation.