Furosemid administration to patients with intracranial hypertension of tumour genesis was associated with temporal regression of general cerebral symptoms, coinciding in time with the period marked by a decrease in cerebrospinal fluid pressure. A correlation between the magnitude of this decrease and the furosemid-induced elevated secretion of urine containing chlorine and sodium was established. Restoration of the liquid lost from the body following drug administration was not accompanied by either a fall in the cerebrospinal fluid pressure or a change in the intensity of general cerebral symptoms. The action of furosemid on intracranial pressure is explained by a reduction in the central venous pressure, by an increased outflow of the venous blood from the cranial cavity as well as by its diminished volume. Concomitant administration of large quantities of water lowers or completely precludes the hypotensive action of the agent on intracranial pressure and, thus, is considered unadvisable.