What can BeppoSAX tell us about X-ray spectra of BL Lacs?

The wide energy band of BeppoSAX, together with its good energy resolution, offers the opportunity to investigate the overall X-ray spectra of BL Lacs, in order to measured in detail their shape, to establish where the Compton component becomes dominant over the synchrotron component. We present here preliminary results from the first year of BeppoSAX observations for a sample of soft X-ray selected BL Lacs. Ten XBL have been observed and analyzed so far: variability with respect to previous observations is very common, spectra are generally well fitted by a single power law, although a few examples of more complex spectra are present. We show BeppoSAX spectra and compare the results on the correlation between the X-ray slope and the peak frequency of the overall spectral energy distribution with those for a sample of radio selected BL Lacs.