  We investigate the single and pair production of new heavy leptons via string
inspired $E_{6}$ model at future linear colliders. Signal and corresponding
backgrounds for these leptons are studied. We have found that single production
of heavy leptons is more relevant than that of pair production, as expected.
For a maximal mixing value of 0.1, the upper mass limits of 2750 GeV in the
single case and 1250 GeV in the pair production case are obtained at
$\sqrt{s}=3$ TeV collider option.
