  The gamma-ray emission of the blazar Markarian 421 above 250 GeV has been
observed by the CAT Cherenkov imaging telescope since December, 1996. We report
here results on the source variability up to April, 1998, with emphasis on the
1998 campaign. For the flaring periods of this year, the energy spectrum was
derived from 330 GeV up to 5.2 TeV: it is very well represented by a simple
power law, with a differential spectral index of 2.96 +/- 0.13.
