ABSTRACT.We report studies in which the amplitude of the cardiac‐synchronous change in transcephalic impedance, ΔZ, has been used in the investigation of cerebral haemodynamics in newborn babies. Three clinical situations, in which cerebral blood flow might be expected to change, have been studied. The impedance signal, ΔZ, decreased in size during a tension pneumothorax, increased slightly with feeding, and, during an exchange transfusion of an asphyxiated baby, there was a consistent increase in the size of the signal during infusion of blood and a decrease in size as blood was withdrawn. This method may be useful for the continuous study of cerebral haemodynamics in the preterm baby over prolonged peri