  To date, only two extragalactic objects have been firmly established as very
high-energy gamma-ray sources in the Northern sky: these are the two blazars
Markarian 501 and Markarian 421. This paper reviews the most striking results
obtained from these sources by the CAT atmospheric Cherenkov imaging telescope,
with a particular emphasis on the 1999-2000 and 2000-2001 observation campaigns
of Markarian 421.
