It is well know that blood-brain barrier (BBB) is an impermeable morphological structure for proteins and for antibodies in particular. However, this type of transmembrane transport has got high practical interest, and especially in connection with targeting transport of some drugs, radionuclides and other biologically active substances into the brain cells.The human hydrophobized and nonhydrophobized antibodies against gliofibrillar acid protein (GFAP) and α 2 -brain specific glycoprotein (α 2 GP) were used for study of their trans-BBB transport. The Fab-fragments of anti GFAP and α 2 GF antibodies were modified by stearoil-chloride in the system of reversed micelles in aerosol OOT in octane. Modified and nonmodified I 1 2 5 marked Fab-fragments of the anti GFAP and α 2 GP antibodies were administered to rats by the intracordial injection. The distribution of the above mentioned Fab-fragments in tissues was studied by scanning in γ-camera (Compu Gamma LKB, Sweden).The accumulation of the hydrophobized Fab-fragments in the brain tissue was observed. In addition to this, it was noticed that the amount of the mark in 1 g of the tissue exceeded on 55% the total mark amount in all organs studied. The phenomenon of selective accumulation of the mark can be explained by rather specific Fab-fragment contact and interaction with GFAP and α 2 GP. In contrast, nonhydrophobized Fab-fragments did not go through the BBB and they were not accumulated in the brain tissue.We assume that the use of the fatty acylation for the artificial hydrophobization of Fab-fragments of antibodies can enhance their capability to penetrate through the cell membranes and BBB, in particular.