  We employ a 3 flavor NJL model to stress some general remarks about the QCD
critical line. The dependence of the critical curve on $\mu_q=(\mu_u+\mu_d)/2$
and $\mu_I=(\mu_u-\mu_d)/2$ is discussed. The quark masses are varied to
confirm that, in agreement with universality arguments, the order of transition
depends on the number of active flavors $N_f$. The slope of the critical curve
vs. chemical potential is studied as a function of $N_f$. We compare our
results with those recently obtained in lattice simulations to establish a
comparison among different models.
