  The relaxation times of particle numbers in hot hadronic matter with
vanishing baryon number are estimated using the ideal gas approximation and
taking into account resonance decays and annihilation processes as the only
sources of particle number fluctuations. Near the QCD critical temperature the
longest relaxation times turn out to be of the order of 10 fm and grow roughly
exponentially to become of the order of $10^{3}$ fm at temperatures around 100
MeV. As a consequence of such long relaxation times, a clear departure from
chemical equilibrium must be observed in the momentum distribution of secondary
particles produced in high energy nuclear collisions.
