  The measured particle ratios in central heavy-ion collisions at RHIC-BNL are
investigated within a chemical and thermal equilibrium chiral SU(3)
\sigma-\omega approach. The commonly adopted noninteracting gas calculations
yield temperatures close to or above the critical temperature for the chiral
phase transition, but without taking into account any interactions. Contrary,
the chiral SU(3) model predicts temperature and density dependent effective
hadron masses and effective chemical potentials in the medium and a transition
to a chirally restored phase at high temperatures or chemical potentials. Three
different parametrizations of the model, which show different types of phase
transition behaviour, are investigated. We show that if a chiral phase
transition occured in those collisions, ''freezing'' of the relative hadron
abundances in the symmetric phase is excluded by the data. Therefore, either
very rapid chemical equilibration must occur in the broken phase, or the
measured hadron ratios are the outcome of the dynamical symmetry breaking.
Furthermore, the extracted chemical freeze-out parameters differ considerably
from those obtained in simple noninteracting gas calculations. In particular,
the three models yield up to 35 MeV lower temperatures than the free gas
approximation. The in-medium masses turn out differ up to 150 MeV from their
vacuum values.
