Guidelines for the clinical indications for measuring pH and blood gas values in fetal blood, the procedures of blood sampling and measurement and some reference values for the evaluation of the data are given. They cover: prenatal sampling of blood from the umbilical vessels in conjunction with cordocentesis, intra partum sampling of fetal capillary blood by skin puncture of the presenting part, post partum sampling of blood from a clamped section of the umbilical cord and general analytical techniques.