  We consider single production of leptoquarks (LQ's) at $e^+e^-$ and
$\gamma\gamma$ colliders, for two values of the centre-of-mass energy,
$\sqrt{s}=500$ GeV and 1 TeV. We find that LQ's which couple within the first
generation are observable for LQ masses almost up to the kinematic limit, both
at $e^+e^-$ and $\gamma\gamma$ colliders, for the LQ coupling strength equal to
$\alpha_{em}$. The cross sections for single production of $2^{nd}$- and
$3^{rd}$-generation LQ's at $e^+e^-$ colliders are too small to be observable.
In $\gamma\gamma$ collisions, on the other hand, $2^{nd}$-generation LQ's with
masses much larger than $\sqrt{s}/2$ can be detected. However,
$3^{rd}$-generation LQ's can be seen at $\gamma\gamma$ colliders only for
masses at most $\sim\sqrt{s}/2$, making their observation more probable via the
pair production mechanism.
