  If a heavy Dirac monopole exists, the light-to-light scattering below the
monopole production threshold is enhanced due to strong coupling of monopoles
to photons. At the next Linear Collider with electron beam energy 250 GeV this
photon pair production could be observable at monopole masses less than 2.5-6.4
TeV in the $e^+e^-$ mode or 3.7-10 TeV in the $\gamma\gamma$ mode, depending on
the monopole spin. At the upgraded Tevatron such an effect is expected to be
visible at monopole masses below 1-2.5 TeV. The strong dependence on the
initial photon polarizations allows to find the monopole spin in experiments at
$e^+e^-$ and $\gamma\gamma$ colliders. We consider the $Z\gamma$ production and
the $3\gamma$ production at $e^+e^-$ and $pp$ or $p\bar{p}$ colliders via the
same monopole loop. The possibility to discover these processes is
significantly lower than that of the $\gamma\gamma$ case.
