6H-SiC epitaxial layers on a substrate with irregular distribution of dislocations with density 10(4)-10(5) cm(-2) have been grown by vacuum sublimation. X-ray and optical methods have been used to study structural defects in 6H-SiC substrates and epitaxial layers. It is shown that during layer growth the structural perfection is improved as compared with the initial state of the substrate, namely, the dislocation density decreases and fine pores are overgrown. With increasing layer thickness, this process becomes more pronounced.