  We study the effects of virtual leptoquarks on charged current and neutral
current processes at the $ep$ collider HERA. We present the areas of parameter
space that can be excluded at HERA by searching for deviations from Standard
Model expectations. The best results are obtained by examining the ratio of
neutral current to charged current cross sections, $R=\sigma_{NC}/\sigma_{CC}$,
where, with $200\inpb$ of integrated luminosity for unpolarized $e^-$ and $e^+$
beams, HERA can search for leptoquarks with masses up to $\sim 800\gev$, with
leptoquark coupling strengths of order $\alpha_{em}$.
