  We investigate the possible effects that deviations from kinetic equilibrium
can have on massive particles as they decouple from chemical equilibrium.
Different methods of solving the Boltzmann equation yield significantly
different relic number densities of such particles. General considerations
concerning the Dirac or Majorana structure of the particles are discussed. It
is shown that non-equilibrium effects are small for particles decoupling while
strongly non-relativistic, as will be the case for most cold dark matter
candidates.
