  The results of a comprehensive study of the cluster environments and
black-hole masses of an optically matched sample of radio-loud and radio-quiet
quasars are presented. No evidence is found for a difference in large-scale
environments, with both quasar classes found to be located in clusters of Abell
class $\sim0$ . Conversely, virial black-hole mass estimates based on
H$_{\beta}$ line-widths show a clear difference in the quasar black-hole mass
distributions. Our results suggest that a black-hole mass of
$\sim10^{9}\Msolar$ is required to produce a powerful radio-loud quasar, and
that it is black-hole mass and accretion rate which hold the key to the
radio-loudness dichotomy.
