  The dynamics of the Einstein-Vlasov equations for a class of cosmological
models with four Killing vectors is discussed in the case of massive particles.
It is shown that in all models analysed the solutions with massive particles
are asymptotic to solutions with massless particles at early times. It is also
shown that in Bianchi types I and II the solutions with massive particles are
asymptotic to dust solutions at late times. That Bianchi type III models are
also asymptotic to dust solutions at late times is consistent with our results
but is not established by them.
