  ROSAT observations of a homogeneous sample of radio--selected BL Lac objects
are presented. Results of a detailed spectral analysis in the soft 0.1-2.0 keV
energy range are discussed and compared with similar previously published
results. The X--ray spectral shape is discussed in relation to the overall
energy distribution with particular emphasys on the high energy gamma--ray
emission recently detected by CGRO--EGRET for about half of the objects in the
sample. Dividing the objects in our sample on the basis of the radio to X--ray
flux ratio (alpha_rx) we show that objects with alpha_rx > 0.75 have flatter
X--ray spectra and are likely to be stronger gamma--ray emitters than objects
with alpha_rx < 0.75. Moreover we note that the value of the peak energy of the
synchrotron component, in a E * F(E) plot, correlates with alpha_rx and
alpha_x.
