The author studied biochemical variations in the blood and the cerebrospinal fluid of thirty-nine uremic patients. The studies included the alkali reserve, most of the nitrogenous fractions of the protein metabolism ordinarily determined in the blood, the inorganic phosphorus, K, Ca, the chlorides, Na, cryoscopy, sugar, cholesterol and lactic acid. The simultaneous study of the blood and the cerebrospinal fluid is valuable from both the diagnostic and the therapeutic points of view. Thus, data obtained from the group of patients suffering from "azotemic" uremia, cases characterized by the disturbance of the nitrogen excretory function without a disturbance of the acid excretory function and without any manifestation of disturbance of the permeability of the hemato-encephalic barrier, permitted the author to draw the conclusion that the process can be reversed by elimination of the causes giving rise to accumulation of nitrogenous waste products, as, for example, infection or dietetic disorder. In another