  We study the susceptibilities of quark number, isospin number and electric
charge in numerical simulations of lattice QCD at high temperature and density.
We discuss the equation of state for 2 flavor QCD at non-zero temperature and
density. Derivatives of $\ln Z$ with respect to quark chemical potential
$(\mu_q)$ are calculated up to sixth order. From this Taylor series, the
susceptibilities are estimated as functions of temperature and $\mu_q$.
Moreover, we comment on the hadron resonance gas model, which explains well our
simulation results below $T_c$.
