  A new Planckian distribution for cosmologies with photon creation is derived
using thermodynamics and semiclassical considerations. This spectrum is
preserved during the evolution of the universe and compatible with the present
spectral shape of the cosmic microwave background radiation(CMBR). Accordingly,
the widely spread feeling that cosmologies with continuous photon creation are
definitely ruled out by the COBE limits on deviation of the CMBR spectrum from
blackbody shape should be reconsidered. It is argued that a crucial test for
this kind of cosmologies is provided by measurements of the CMBR temperature at
high redshifts. For a given redshift $z$ greater than zero, the temperature is
smaller than the one predicted by the standard FRW model.
