Tensile drawing of the poly(ethylene terephthalate) (PET) samples in semidilute solutions of poly(ethylene oxide) (PEO) with the molecular mass ranging from 4 x 10(4) to 1 x 10(6) proceeds via the mechanism of solvent crazing. This process is accompanied by the penetration of PEO into the porous structure of crazes, and this conclusion is proved by the data on the composition of the resultant blends as well as by the direct electron microscopic observations. Effective diameter of pores in the nanoporous structure of the solvent-crazed PET samples is estimated by the method of pressure-driven liquid permeability. Structure of PEOs is studied by the methods of dynamic light scattering and capillary viscometry as a function of the molecular mass and polymer concentration in the solutions. Penetration of PEO into the solvent-crazed nanoporous structure proceeds under so-called "confined" conditions when the hydrodynamic radius of a polymer coil is comparable or higher than the effective dimensions of pores in the crazes. Penetration of the PEO macromolecules into the porous structure of the solvent-crazed PET-based sample via diffusion under the action of the concentration gradient is compared with the flow-assisted penetration in the course of the tensile drawing of the PET samples in the PEO solutions. Content of PEO in the pores of the solvent-crazed polymer samples is higher than that in the surrounding solution, and this fact can be explained by the adsorption of PEO on the highly developed surface of the fibrillated polymer in crazes. Penetration of PEO into the porous structure upon tensile drawing proceeds much quicker (minutes) as compared with the attainment of the equilibrium content of the polymer under the action of the concentration gradient (days).