  We reanalyze the conditions under which we have a primordial thermal
population of axions. Compared with previous studies, we find other processes,
involving gluons and quarks, that dominate at high temperatures. We conclude
that if the Peccei-Quinn scale fulfills $F_a < 1.2 \times 10^{12} \GeV$ there
is thermal axion production. In this case, a period in the early universe
exists where axions interact with the QCD plasma and we point out that
non-thermal axions produced before the end of this period will thermalize. This
could lead to a reduction of the expected density of axions from string decay
in models with $F_a < 1.2 \times 10^{12} \GeV$.
