  We present results from several XMM-Newton observations of the radio loud
Narrow-line Seyfert 1 galaxy (NLS1) PKS 0558-504. We find evidence for strong
and persistent X-ray variability, both on short and long time-scales. On short
time scales of ~2 hours the source varies smoothly by 15-20%; long term
variations by a factor of >2 could not be resolved in the relatively short
exposures: we find the source mostly in a `low' state, in 2 out of the 11
observations in a `high state'. X-ray flares seem to be recurrent with a time
scale of ~24 ksec which, if interpreted as the Keplerian time scale in the
disc, would place the emission region just outside the last stable orbit. The
X-ray spectrum of PKS 0558-504 can be well fitted by two Comptonization
components, one at moderate temperatures of kT ~ 4.5 keV and optical depths of
\~ 2, the other at high temperatures kT > 50 keV and low optical depths < 1.0.
These parameters are, however, subject to large errors due to the inherent
degeneracy of the Comptonization models. Flux variations of the source are
caused by changes of the colder component only, the hot component with
parameters very similar to those of BLS1 galaxies, stays constant. All results
fit nicely the picture that NLS1 galaxies are lower mass objects, accreting
close to the Eddington rate emitting X-rays from a very active magnetically
powered accretion disc corona.
