  In the framework of inflationary cosmology I study some aspects of
nonequilibrium thermodynamics for the matter field fluctuations. The
thermodynamic analysis is developed for de Sitter and power - law expansions of
the universe. In both cases, I find that the heat capacity is negative leading
respectively, to exponential and superexponential growth for the number of
states in the infrared sector for de Sitter and power-law expansions of the
universe. The spectrum for the matter field fluctuations can be understood from
the background effective temperature when the horizon entry.
