  We have studied the distribution of $B_J<20.5$ galaxies from the ROE/NRL
COSMOS/UKST catalogue around two samples of $z>0.3$ QSOs with similar redshift
distributions. The first sample is formed by 144 radio-loud QSOs from the
Parkes Catalogue, and the other contains 167 optically selected QSOs extracted
from the Large Bright Quasar Survey. It is found that there is a $\approx
99.0%$ significance level excess of COSMOS/UKST galaxies around the PKS QSOs,
whereas there is a marginal defect of galaxies around the LBQS QSOs. When the
distribution of galaxies around both samples is compared, we found that there
is an overdensity of galaxies around the PKS sample with respect to the LBQS
sample anticorrelated with the distance from the QSOs at a $99.7%$ significance
level. Although this result apparently agrees with the predictions of the
double magnification bias, it is difficult to explain by gravitational lensing
effects alone; dust in the foreground galaxies and selection effects in the
detection of LBQS QSOs should be taken into account. It has been established
that the lines of sight to PKS flat-spectrum QSOs go through significatively
higher foreground galaxy densities than the directions to LBQS quasars, what
may be partially related with the reported reddening of PKS QSOs.

Astrophysics