  The Italian-Dutch satellite for X-ray Astronomy BeppoSAX is successfully
operating on a 600 km equatorial orbit since May 1996. We present here the
in-flight performances of the Gamma Ray Burst Monitor experiment during its
first year of operation. The GRBM is the secondary function of the four CsI(Na)
slabs primarily operating as an active anticoincidence of the PDS hard X-ray
experiment.. It has a geometric area of about 4000 cm2 but, due to its location
in the core of the satellite its effective area is dependent on the energy and
direction of the impinging photons. A dedicated electronics allows to trigger
on cosmic gamma-ray bursts. When the trigger condition is satisfied the light
curve of the event is recorded from 8 s before to 98 s after the trigger time,
with a maximum time resolution of 0.48 ms, in an energy band of 40-700 keV.
