  Some properties of cosmological models with matter creation are investigated
in the framework of the Friedman-Robertson-Walker (FRW) line element. For
adiabatic matter creation, as developed by Prigogine and coworkers, we derive a
simple expression relating the particle number density $n$ and energy density
$\rho$ which holds regardless of the matter creation rate. The conditions to
generate inflation are discussed and by considering the natural
phenomenological matter creation rate $\psi =3 \beta nH$, where $\beta$ is a
pure number of the order of unity and $H$ is the Hubble parameter, a minimally
modified hot big-bang model is proposed. The dynamic properties of such models
can be deduced from the standard ones simply by replacing the adiabatic index
$\gamma$ of the equation of state by an effective parameter $\gamma_{*} =
\gamma (1 - \beta)$. The thermodynamic behavior is determined and it is also
shown that ages large enough to agree with observations are obtained even given
the high values of $H$ suggested by recent measurements.
