X-rays and accretion discs as probes of the strong gravity of black holes

The observations and interpretation of broad iron lines in the X-ray spectra of Seyfert 1 galaxies are reviewed. The line profiles observed from MCG--6-30-15 and NGC 3516 show extended red wings to the line explained by large gravitational redshifts. The results are consistent with the emission expected from an X-ray irradiated flat accretion disc orbiting very close to a black hole. Results from XMM-Newton and Chandra are presented and the possibility of broad oxygen lines discussed.