  PKS 0537-441, a bright gamma-ray emitting blazar, was observed at radio,
optical, UV and X-ray frequencies during various EGRET pointings, often
quasi-simultaneously. In 1995 the object was found in an intense emission state
at all wavelengths. BeppoSAX observations made in 1998, non-simultaneously with
exposures at other frequencies, allow us to characterize precisely the spectral
shape of the high energy blazar component, which we attribute to inverse
Compton scattering. The optical-to-gamma-ray spectral energy distributions at
the different epochs show that the gamma-ray luminosity dominates the
bolometric output. This, together with the presence of optical and UV line
emission, suggests that, besides the synchrotron self-Compton mechanism, the
Compton upscattering of photons external to the jet (e.g., in the broad line
region) may have a significant role for high energy radiation. The
multiwavelength variability can be reproduced by changes of the plasma bulk
Lorentz factor. The spectrum secured by IUE in 1995 appears to be partially
absorbed shortward of ~1700 A. However, this signature is not detected in the
HST spectrum taken during a lower state of the source. The presence of
intervening absorbers is not supported by optical imaging and spectroscopy of
the field.
