  Warm inflation is an interesting possibility of describing the early
universe, whose basic feature is the absence, at least in principle, of a
preheating or reheating phase. Here we analyze the dynamics of warm inflation
generalizing the usual slow-roll parameters that are useful for characterizing
the inflationary phase. We study the evolution of entropy and adiabatic
perturbations, where the main result is that for a very small amount of
dissipation the entropy perturbations can be neglected and the purely adiabatic
perturbations will be responsible for the primordial spectrum of
inhomogeneities. Taking into account the COBE-DMR data of the cosmic microwave
background anisotropy as well as the fact that the interval of inflation for
which the scales of astrophysical interest cross outside the Hubble radius is
about 50 e-folds before the end of inflation, we could estimate the magnitude
of the dissipation term. It was also possible to show that at the end of
inflation the universe is hot enough to provide a smooth transition to the
radiation era.
