By calculating free energies, several published interatomic interaction potentials for iron are investigated with respect to the stability of the low-temperature bcc phase and the high-temperature fcc phase. These are empirical many-body potentials for use in atomistic simulation. We find that in all of these potentials—except one—the bcc phase is the stable crystal structure for all temperatures up to the melting point. However, several potentials exhibit a metastable fcc phase in the sense that the fcc structure corresponds to a local minimum of the free energy.