A controlled prospective study of the differential effects of intrapartum fetal monitoring on mothers and infants has been conducted at Denver General Hospital, Denver, Colorado. A total of 690 high-risk obstetric patients in labor were randomly assigned to one of three monitoring groups--auscultation, electronic fetal monitoring alone, or electronic monitoring with the option to scalp sample. There were no differences in immediate infant outcomes in any measured category (Apgar scores, cord blood gases, neonatal death, neonatal morbidity, nursery course) among the three groups. There were no differences in rates of infant or maternal infections. The cesarean section rate was markedly increased in the electronically monitored groups, especially in the electronically monitored alone (18%) as compared with the auscultated (6%) (P less than 0.005). In this controlled trial electronic monitoring did not improve neonatal outcomes and the mothers were at increased risk of cesarean section.