Evidence is presented for widespread relativistic effects in the central regions of active galactic nuclei (AGN). A sample of 18 Seyfert 1 galaxies observed by ASCA show iron Kα emission which is resolved, with mean full width at half maximum (FWHM) ~ 50,000 km s−1 for a Gaussian profile. However, many of the line profiles are asymmetric. A strong red wing is indicative of gravitational redshifts close to a central black hole, and accretion-disk models provide an excellent description of the data. Such observations probe the innermost regions of AGN, and arguably provide the best evidence yet obtained for the existence of supermassive black holes in the centers of active galaxies.