  We report results on the timing and spectral analysis of observations of the
millisecond pulsar PSR B1821-24 with RXTE, BeppoSAX and Chandra. The X-ray
light curve is characterized by two narrow peaks at a phase distance of
0.452+/-0.002. The average pulsed emission, over the range 1.6-20 keV, is well
represented by a single power law with a photon index alpha=1.30 +0.05 -0.02
and unabsorbed (2-10 keV) pulsed X-ray flux of 3.9x10^(-13) erg cm^(-2) s^(-1).
We searched for a possible bunching of X-ray photons to verify if the X ray
emission has a time structure similar to that of giant pulses and found a
negative result.
