Using the Nambu-Jona-Lasinio (NJL) model we study responses of the pion and kaon masses to changes in the chemical potential,∂m/∂&mgr;,at zero and finite chemical potential. We find that the behavior of∂m/∂&mgr;for the pion is quite different from that for the kaon. Our results can give a clue for future studies of∂m/∂&mgr;on the lattice. ©2001 American Institute of Physics.