  We present the results of an ASCA observation of the high redshift flat
spectrum radio quasar S5 0836+710. The $\sim 0.4-10$ keV X-ray spectrum is
remarkably flat with $\Gamma \sim 1.4$ and substantial intrinsic absorption at
low energy. The spectral slope was found to be in good agreement with the
non--simultaneous ROSAT PSPC observations while no evidence of intrinsic
absorption has been found in the PSPC spectrum. Our results suggest time
variability of the absorbing material on timescales less than five months in
the source rest--frame.
