Simultaneous monitoring of fetal tissue pH (t-pH) and transcutaneous carbon dioxide (Tc-PCO2) was performed in 30 labours. Both t-pH and Tc-PCO2 at delivery were positively correlated with pH (r = 0.69) and PCO2 (r = 0.68) of the umbilical artery blood. A tissue/transcutaneous standard base excess (t-SBE) was derived from the t-pH and the Tc-PCO2 and calculated for 13 fetuses at delivery; there was a correlation with standard base excess of umbilical artery blood. An analysis of t-pH and Tc-PCO2 changes during the last hour of labour revealed that only infants who were born with decreased pH of the umbilical artery blood had decreasing t-SBE, while all others had a constant t-SBE.