  Cross sections involving massive Dirac or Majorana neutrinos usually differ
only by terms which are suppressed by the smallness of the neutrino mass. The
process $e^+e^-\to\nu\nu$, however, is an example in which the two differential
cross sections are quite distinct even in the limit $m_\nu\to 0$ as long as
$m_\nu\not=0$. I discuss the cause of this phenomenon and comment on strategies
to identify processes with quite different Majorana and Dirac neutrino signals.
