  The problem of CP conservation and CP violation for two heavy neutrinos
production in $e^+e^-$ interaction is considered. Very convenient way of
parametrization of the neutrino mass matrix, from which necessary and
sufficient condition for CP conservation easily follows, is presented. Contrary
to the Kobayashi-Maskawa mechanism, the effects of CP violation in the lepton
sector with Majorana neutrinos can be very large. Change of the total cross
section caused by CP violation can be much larger then the cross section
itself.
