  Strangeness plays an important role in the study of quark matter since it
indicates the rate at which new particles are being produced and therefore
provides information about the degree of chemical equilibration reached in
heavy ion collisions. It is shown that ratios provide an excellent method for
determining the temperature and the chemical potential since many theoretical
uncertainties cancel out. All indications are that particle abundances are very
close to chemical equilibrium. The amount of strangeness present in $S-S$
collisions is very close to the one corresponding to chemical equilibrium.
Deviations are at the 30% level.
