  The arguments for the possibility of violation of P and CP symmetries of
strong interactions at finite temperature are presented. A new way of observing
these effects in heavy ion collisions is proposed -- it is shown that parity
violation should manifest itself in the asymmetry between positive and negative
pions with respect to the reaction plane. Basing on topological considerations,
we derive a {\it lower} bound on the magnitude of the expected asymmetry, which
may appear within the reach of the current and/or future heavy ion experiments.
