A special technique for "en face" artery endothelium preparation is intioduced, with which the nucleus labelled by ~3H—TdR can be seen with light microscopy. The endothelial regeneration canbe quantitatively analysed by calculating the labelling rate of endothelial ceils. The endothelial injury in quails with hypercholesterolemia was studied by this method. The more injury, the more cell regeneration. It is obvious that this method can be used in the study of any kind of endothelial injury.