Various tests for the presence of absorbing matter in spiral galaxies are considered: the dependence of central surface brightness on angle of inclination, the surface brightness of partially overlapping galaxies in the overlap region, and the dependence of galactic isophotal radii on increasing inclination to the line of sight. It is shown that the nuclei of spiral galaxies are optically thick, but the absorption falls rapidly with increasing distance from the center and at the distance r almost-equal-to 0.5R25 the total absorption is only a few tenths of a stellar magnitude (A(B) <1m).