  Virial black-hole mass estimates are presented for 12698 quasars in the
redshift interval 0.1<z<2.1, based on modelling of spectra from the Sloan
Digital Sky Survey (SDSS) first data release . The black-hole masses of the
SDSS quasars are found to lie between $\simeq10^{7}\Msun$ and an upper limit of
$\simeq 3\times 10^{9}\Msun$, entirely consistent with the largest black-hole
masses found to date in the local Universe. The estimated Eddington ratios of
the broad-line quasars (FWHM \geq2000 km s^{-1}) show a clear upper boundary at
L_{bol}/L_{Edd}~1, suggesting that the Eddington luminosity is still a relevant
physical limit to the accretion rate of luminous broad-line quasars at $z\leq
2$. By combining the black-hole mass distribution of the SDSS quasars with the
2dF quasar luminosity function, the number density of active black holes at
$z\simeq 2$ is estimated as a function of mass. By comparing the estimated
number density of active black holes at $z\simeq 2$ with the local mass density
of dormant black holes, we set lower limits on the quasar lifetimes and find
that the majority of black holes with mass $\geq 10^{8.5}\Msun$ are in place by
$\simeq 2$.
