  We present the first results for lattice QCD at finite temperature $T$ and
chemical potential $\mu$ with four flavors of Wilson quarks. The calculations
are performed using the imaginary chemical potential method at $\kappa=0$,
0.001, 0.15, 0.165, 0.17 and 0.25, where $\kappa$ is the hopping parameter,
related to the bare quark mass $m$ and lattice spacing $a$ by
$\kappa=1/(2ma+8)$. Such a method allows us to do large scale Monte Carlo
simulations at imaginary chemical potential $\mu=i \mu_I$. By analytic
continuation of the data with $\mu_I < \pi T/3$ to real values of the chemical
potential, we expect at each $\kappa\in [0,\kappa_{chiral}]$, a transition line
on the $(\mu, T)$ plane, in a region relevant to the search for quark gluon
plasma in heavy-ion collision experiments. The transition is first order at
small or large quark mass, and becomes a crossover at intermediate quark mass.
