FIELD : medicine.SUBSTANCE : invention relates to medicine, namely to pharmacology and clinical pharmacology. Method for evaluating the functional activity of glycoprotein-P in the blood-brain barrier according to the pharmacokinetics of its marker substrate fexofenadine includes the intravenous administration of fexofenadine to laboratory animals with the subsequent calculation of the ratio of the area under the curve “concentration of fexofenadine in plasma – time” to the area under the curve “concentration of fexofenadine in the cerebral cortex – time” – AUC0-t-brain/AUC0-t-plasma.EFFECT : invention can be used with the aim of assessment of the functional activity of glycoprotein-P (Pgp) in the blood-brain barrier for effective and safe pharmacotherapy of a number of neurological diseases.1 cl, 1 dwg