Previously, the various components of fetal acid-base state during labour could only be estimated discontinuously by fetal blood sampling, or continuously by monitoring of a single component. This is the first report describing simultaneous continuous monitoring of the tissue pH, the transcutaneous carbon dioxide tension and on-line calculation of the tissue-standard base excess (t-SBE) of the human fetus during labour. In seven uncomplicated deliveries t-SBE was increasing or constant, thus indicating no fetal hypoxia. When a more reliable tissue pH electrode becomes available, t-SBE calculation may become a valuable tool in the management of high-risk labours.