  We briefly discuss the theoretical implications of recent detections of
gamma-ray bursts (GRBs) by BSAX. Relativistic shock wave theories of fireball
expansion are challenged by the wealth of X-ray, optical and radio data
obtained after the discovery of the first X-ray GRB afterglow. BSAX data
contribute to address several issues concerning the initial and afterglow GRB
emission. The observations also raise many questions that are still unsolved.
The synchrotron shock model is in very good agreement with time-resolved
broad-band spectra (2-500 keV) for the majority of GRBs detected by BSAX.
