  ROSAT observations of a large sample of bright gamma-ray (E > 100 MeV)
blazars are presented. Results of a detailed spectral analysis in the soft
$\sim$ 0.1-2.0 keV energy range are discussed in relation to the overall energy
distribution with particular emphasis on the relation between X-ray and
gamma-ray properties. A significant anti-correlation between X-ray and
gamma-ray spectral shapes of flat radio spectrum quasars (FSRQ) and BL Lacs has
been discovered. A different shape in the overall energy distributions from
radio to gamma-ray energies between FSRQ and BL Lacs is also implied by the
correlation of their broad-band spectral indices $\alpha_{ro}$ and $\alpha_{x
\gamma}$. Both the above correlations can be explained if both the IR to UV
emission and the hard X-ray to gamma-ray emission originate from the same
electron population, via, respectively, the synchrotron process and the inverse
Compton mechanism. We suggest that a key parameter for understanding the
overall energy distributions of both classes of objects is the energy at which
the synchrotron emission peaks in a $\nu-\nu F(\nu)$ representation.
