Measurement of fetal scalp blood pH aids detection of fetal asphyxia. The investigation is done on patients whose fetus is at increased risk of death. Special care in collection and measurement of scalp blood pH is necessary to obtain satisfactory results. A change of 0.05 pH unit is significant. Acidosis is present when scalp pH is > 7.25. A severe acidosis, pH > 7.10, indicates a worse fetal prognosis. Fetal metabolic acidosis is the commonest type of acidosis, but is less hazardous than asphyxial acidosis. Fetal metabolic acidosis is associated with use of drugs, PET [pre-eclamptic toxemia], fetal growth retardation, amniotomy and maternal starvation. The possibility of transient acidosis needs to be taken into account when interpreting fetal scalp pH measurements. Fetal scalp blood studies have helped in defining the influence upon fetal condition of maternal hyperoxygenation, duration of birth, maternal posture and the influence of drugs on fetal condition. A controlled trial has shown that fetal intensive care, routine FHR [fetal heart rate] monitoring and selected fetal scalp blood pH measurement in a high risk group is associated with improved biochemical and neurological status of the newborn. Over the last 8 yr there has been a significant reduction of intrapartum anoxic stillbirths. One of the probable reasons for this reduction in intrapartum stillbirths is introduction of fetal diagnostic techniques. FHR monitoring is more help to the clinical obstetrician than scalp sampling.