  Axions with variable masses, in the context of a scalar--tensor gravity
theory, give a large entropy production during the matter era. The subsequent
axion dilution is proportional to their present energy density. Depending on
the parameters ($\beta_I,\beta_V$) of the model, this dilution relaxes or even
eludes the cosmological bound on the axion mass, therefore opening the
so--called ``axion window".
