  We use the 2PI effective action of a relativistic scalar field theory to
derive kinetic equations for a Bose-condensed system near the phase
transition.We start from equations of motion derived within a 1/N-expansion at
NLO. In taking the non-relativistic limit we obtain a generalized
Gross-Pitaevskii equation for the condensate field. Within the Popov
approximation we explicitly compute the collision term up to order g^2 using
the Kadanoff-Baym formalism. For the sake of self-consistency we derive in the
same way a Boltzmann equation for the non-condensate distribution function. The
final results are in agreement to those previously obtained by Griffin, Nikuni
and Zaremba and by Stoof.
