In the article some concerns of the histochemical evaluation of the endothelium structure in vessels of the upper and lower jaws in its normal state and against the background of the periodontium inflammation have been considered. The experiment has been conducted on the rams that have been injected the corticosteroid remedy into their gum around the dental cervix of the lower incisors for further modeling of the experimental periodontitis. Within the experiment the animals have been given a porridge-like food for avoiding the self-cleaning of teeth. The received data have shown that the endothelial structural indices have been different for the upper and the lower jaw against the background of the periodontitis in the gum vessels. This difference is connected to the cytostructural of cells, their thickness, and the number of mitochondria, Golgi complex, endothelium reticulum, the connection between the nucleus and the cytoplasm and the different heterochromatin amount in the nucleus. By the periodontist the pathological changes have been revealed not only in the endothelium circle but also in the pericytes which presents the complex hystovascular reaction of the microcirculatory channel of the periodontium tissues including the disorder in the rheological blood properties as well as the formation of the exudates and the inflammatory cellular infiltrate.