  The masses and emission-line region sizes of Active Galactic Nuclei (AGNs)
can be measured by ``reverberation-mapping'' (measuring the lag of the
emission-line luminosity after changes in the continuum). We use tis technique
to calibrate similar size and mass estimates made by photoionization models of
the AGN line-emitting regions. We compile a sample of 19 AGNs with reliable
reverberation and spectroscopy data, twice the number available previously. The
data provide strong evidence that the BLR size and the emission-line width
measure directly the central mass. Two methods are used to estimate the
distance of the broad emission-line region (BLR) from the ionizing source: the
photoionization method (available for many AGNs but has large intrinsic
uncertainties), and the reverberation method (gives very reliable distances,
but available for only a few objects). The distance estimate is combined with
the velocity dispersion, derived from the broad Hb line profile, to estimate
the virial mass. Comparing the central masses calculated with the reverberation
method to those calculated using a photoionization model, we find a highly
significant, nearly linear correlation. This provides a calibration of the
photoionization method on the objects with presently available reverberation
data, which should enable mass estimates for all AGNs with measured Hb line
width. Comparing the BLR sizes given by the two methods also enables us to
estimate the ionizing EUV luminosity which is directly unobservable. We find it
to be typically ten times the visible (monochromatic luminosity at 5100A). The
inferred Eddington ratio of the individual objects in our sample are 0.001-0.03
(visible luminosity) and 0.01-0.3 (ionizing luminosity).
