  The first set of supermassive black hole mass estimates, published from 1980
to 1984 by E. A. Dibai, are shown to be in excellent agreement with recent
reverberation-mapping estimates. Comparison of the masses of 17 AGNs covering a
mass range from about 10^6 to 10^9 solar masses shows that the Dibai mass
estimates agree with reverberation-mapping mass estimates to significantly
better than 0.3 dex and were, on average, only 0.14 dex (~ 40%) systematically
lower than masses obtained from reverberation mapping. This surprising
agreement with the results of over a quarter of a century ago has important
implication for the structure and kinematics of AGNs and implies that AGNs are
very similar. Our results give strong support to the use of the
single-epoch-spectrum (Dibai) method for investigating the co-evolution of
supermassive black holes and their host galaxies.
