  Using the Nambu--Jona-Lasinio (NJL) model we study chemical potential
response of the pion and kaon masses as a function of temperature and chemical
potential, i.e., dm/d\mu (T, \mu). First, we obtain the responses assuming the
vector-axial vector coupling is zero (g_V=0). Then, we include a non-zero g_V
and study the effects of g_V on the responses. We find that the behavior of
dm/d\mu for the pion is quite different from that for the kaon. It means that
dm/d\mu is much dependent on the mass difference between the two quarks, i.e.,
the u and s quarks (or even between the u and d quarks). Our results may give a
clue to future studies of dm/d\mu on the lattice.
