  We investigate the potentials of high energy lepton-proton colliders to
detect a flavor changing $l-l^{\prime}-Z$ or $l-l^{\prime}-\gamma$ couplings
from the processes $ep\to\mu(\tau)X$ and $\mu p\to \tau X$. For the
$l-l^{\prime}-Z$ coupling we consider string inspired $E_6$ model whereas
$l-l^{\prime}-\gamma$ coupling is analyzed in the framework of anomalous
magnetic moment type interaction (AMMI) model.
