Results are presented on the X-ray properties of 9 high-redshift ( 1.2 < z < 3.4 ) radio-loud quasars ( RLQs ) observed by ASCA ( 10 observations ) and ROSAT ( 11 observations , for a subset of 6 quasars ) .
New ASCA observations of S5 0014+81 ( z = 3.38 ) and S5 0836+71 ( z = 2.17 ) and ROSAT observations of PKS 2126-158 for which results were never presented elsewhere , are included .

A simple model consisting of a power law plus cold , uniform absorption gives acceptable fits to the spectra of all sources .
The ASCA spectra of the 6 brightest objects show evidence for absorption in excess of the Galactic value at a \gg 99 % confidence level .
Comparison with the ROSAT data suggests that absorption has significantly varied ( \Delta N _ { H } \sim 8 \times 10 ^ { 20 } cm ^ { -2 } ) in the case of S5 0836+71 , on a time-scale of \sim 0.8 yr in the quasar frame .
For the remaining 5 sources for which ROSAT spectra were available , the two instruments gave consistent results and the data were combined yielding unprecedent spectral coverage ( typically \sim 0.4-40 keV in the quasar frame ) for high-z quasars .
This allows to put severe limits on several different descriptions of the continuum ( e.g .
broken power law , bremsstrahlung , reflection component ) .
No Fe K \alpha emission line is detected in any of the ASCA spectra .
An absorption edge consistent with Fe K \alpha at the quasar redshift is marginally detected in S5 0014+81 .
Possible origins for the observed low energy absorption are discussed .
In particular , contributions from the molecular clouds and dust present in our Galaxy ( usually disregarded ) are carefully considered .
In the light of the new results for S5 0836+71 and S5 0014+81 , absorption intrinsic to the quasars is considered and discussed .

The average slope obtained from the 8 ASCA spectra in the observed \sim 0.5–10 keV energy band is < \Gamma _ { 0.5 - 10 keV } > \simeq 1.61 \pm 0.04 , with a dispersion \sigma _ { 0.5 - 10 keV } \simeq 0.10 \pm 0.03 .
The average photon index in the observed 2–10 keV band , where the effect of absorption is negligible , is < \Gamma _ { 2 - 10 keV } > \simeq 1.53 \pm 0.05 , with a dispersion \sigma _ { 2 - 10 keV } < \lower 4.558 pt \hbox { $ \kern - 10.7 pt { \sim } $ } 0.12 .
Furthermore , the implications of the present results on the calculations of the contribution of quasars to the cosmic X- and \gamma -ray backgrounds ( XRB and GRB ) are briefly discussed .

\keywords galaxies : active — quasars : general — X-rays : galaxies