  We consider the contributions to $g_\mu-2$ from fourth generation heavy
neutral and charged leptons, $N$ and $E$, at the one-loop level.
Diagrammatically, there are two types of contributions: boson-boson-$N$, and
$E$-$E$-boson in the loop diagram. In general, the effect from $N$ is
suppressed by off-diagonal lepton mixing matrix elements. For $E$, we consider
flavor changing neutral couplings arising from various New Physics models,
which are stringently constrained by $\mu\to e\gamma$. We assess how the
existence of a fourth generation would affect these New Physics models.
