  We present initial results of a numerical investigation of the chiral
symmetry restoring transition in the (3+1)-dimensional Nambu -- Jona-Lasinio
model with both non-zero baryon chemical potential (mu_B) and isospin chemical
potential (mu_I). With non-zero isospin chemical potential, the model suffers
from a sign problem. We proceed in two ways: (i) We perform ``partially
quenched'' simulations in which mu_I is made non-zero only during the
measurement of chiral observables; (ii) We perform full simulations with
imaginary isospin chemical potential with the aim to analytically continue
results to real mu_I.
