  We present a summary of strange particle yields measured by the experiment
NA49 in central Pb+Pb collisions in the beam energy range 20-158 AGeV. The
comparison with thermal hadron model results shows that above 30 AGeV, a
strangeness undersaturation parameter gamma_S must be employed to describe the
data. This suggests a change in the strangeness production mechanism at this
energy. We find that the UrQMD transport model in all cases underpredicts the
observed particle yields.
