  We investigate the consequences of introducing a set of exotic doublet
leptons which couple to the standard model leptons in a minimal way. Through
these additional gauge invariant and renormalizable coupling terms, new sources
of tree-level flavor changing currents are induced via mixing. In this work, we
derive constraints on the parameters that govern the couplings to the exotic
doublets by invoking the current low-energy experimental data on processes such
as leptonic Z decays, $\ell \rightarrow 3 \ell'$, $\ell \rightarrow \ell'
\gamma$, and $\mu$-$e$ conversion in atomic nuclei. Moreover, we have analyzed
the role these doublets play on the lepton anomalous magnetic moments, and
found that their contribution is negligible.
