  A simple formula for the ratio of the number of odd- and even-parity states
as a function of temperature is derived. This formula is used to calculate the
ratio of level densities of opposite parities as a function of excitation
energy. We test the formula with quantum Monte Carlo shell model calculations
in the $(pf+g_{9/2})$-shell. The formula describes well the transition from low
excitation energies where a single parity dominates to high excitations where
the two densities are equal.
