The influence of matter creation processes on the dynamics of the earl
y universe is investigated within a phenomenological approach. By usin
g a balance law for the particle number in addition to the familiar re
lations for viscous fluid cosmologies the whole dynamics is given expl
icitly in terms of the particle production rate. We argue that a suffi
ciently high particle production rate gives rise to an inflationary be
haviour with finite values of temperature and density at the beginning
of the hydrodynamic period of the universe.