  We study the implications of a light tetraquark on the chiral phase
transition at nonzero temperature $T$: The behavior of the chiral and
four-quark condensates and the meson masses are studied in the scenario in
which the resonance $f_{0}(600)$ is described as a predominantly tetraquark
state. It is shown that the critical temperature is lowered and the transition
softened. Interesting mixing effects between tetraquark, and quarkonium
configurations take place.
