  We compute the six oblique parameters $S, T, U, V, W, X$ in a New Physics
Model with an arbitrary number of new fermions, in arbitrary representations of
$SU(2) \times U(1)$, and mixing arbitrarily among themselves. We show that $S$
and $U$ are automatically finite, but $T$ is finite only if there is a specific
relation between the masses of the new fermions and the representations of
$SU(2) \times U(1)$ that they sit in. We apply our general computation to two
illustrative cases.
