Langmuir films of IgG formed at the air-water interface and covalently immobilized on solid supports were studied by means of fluorometry and ellipsometry. Dependencies of monolayer molecular density and thickness on surface pressure were determined. The data obtained make possible a model of the film molecular organization and its dependence on the surface pressure. The films are of monomolecular layer character within the entire range of achievable pressures on the air-water interface as well as on the solid supports. The molecular orientation changes with the pressure. In the monolayer on the air-water interface the molecules are positioned with their Fab-Fab-Fc ploane parallel to the surface at pressures below 20 mN/m; when compressed up to 35 mN/m, they turn by 90 degrees to reach perpendicular position with respect to the surface. Within the range 20 mN/m < pi < 35 mN/m the angle of molecular inclination increases monotonically from 0 degrees to 90 degrees with pressure. The pattern of the orientation-pressure behavior for transferred monolayers is almost the same showing that the film molecular structure does not change upon deposition on to the solid activated substrate.