  We use the Nambu--Jona-Lasinio model to study the effects of the isospin
chemical potential on the QCD phase diagram at nonzero temperature and baryon
chemical potential. We find that the phase diagram is qualitatively altered by
a small isospin chemical potential. There are two first order phase transitions
that end in two critical endpoints, and there are two crossovers at low baryon
chemical potential. These results have important consequences for systems where
both baryon and isospin chemical potentials are nonzero, such as heavy ion
collision experiments. Our results are in complete agreement with those
recently obtained in a Random Matrix Model.
