  We investigate the decay of metastable states with broken CP-symmetry which
have recently been proposed by Kharzeev, Pisarski and Tytgat to form in hot
hadronic matter. We consider the efficiency of the amplification of the
$\eta'$-field via parametric resonance, taking the backreaction into account.
For times of the order $t\approx 10 fm$, we find a particle density of about
$0.7/fm^3$ and a correlation length of $\xi_{max}\approx 2.5 fm$. The
corresponding momentum spectra show a non-thermal behaviour.
