The relationship between different FHR patterns and fetal tissue pH in 68 high-risk gravidas in labor was analyzed. A tissue pH electrode was placed in the fetal scalp and tissue pH recorded on a fetal monitor every 15 seconds along with uterine contractions and continuous fetal heart rate. The tissue pH changes correlated with the FHR patterns in a manner consistent with current concepts of fetal stress. Trend monitoring of fetal tissue pH in labor may prove useful in the management of high-risk patients in labor.