  A search for heavy neutrinos that are isosinglets under the standard
$SU(2)_L$ gauge group is made at center-of-mass energies 130 $< \sqrt{s} <$ 189
GeV with the L3 detector at LEP. Such heavy neutrinos are expected in many
extensions of the Standard Model. The search is performed for the first
generation heavy singlet neutrino, $\mathrm{N}_e$, through the decay mode
$\mathrm{N}_e \to \mathrm{e} + \mathrm{W}$. We set upper limits on the mixing
parameter between the heavy and light neutrino for the heavy neutrino mass
range from 80 GeV to 185 GeV.
