To see if a pulse oximeter can monitor the fetus during labour we recruited 100 Caucasian women in normal uncomplicated labour. Our primary objective was to compare the predictive value of fetal pulse oximetry and cardiotocography using neonatal condition and cord blood acidaemia or hypoxaemia at birth as outcome variables. The fetuses were monitored continuously with a pulse oximeter specifically adapted for fetal use. Five babies had an operative delivery because of an abnormal CTG. Two of these were born in good condition (Apgar score 9 at 1 minute in both cases). The other three babies were delivered in poor condition (Apgar scores of 6 & 9, 5 & 10 and 5 & 10 at 1 and 5 minutes respectively). The oxygen saturation reading only dropped significantly in babies born in poor condition and in one case the drop preempted the CTG changes. These data suggest that pulse oximetry can be adapted to monitor the fetus and has the potential to provide useful information during labour.