  For an exact chiral symmetry which is spontaneously broken at zero
temperature, we show that at nonzero temperature, generally pions travel at
{\it less} than the speed of light. This effect first appears at next to
leading order in an expansion about low temperature. When the chiral symmetry
is approximate we obtain two formulas, like that of Gell-Mann, Oakes, and
Renner, for the static and dynamic pion masses.
