  We calculate the flux of cosmic gamma rays expected {}from the annihilation
of neutralinos in the Galactic halo. Our calculation of the annihilation cross
section to two photons improves the existing calculations by inclusion of exact
one-loop diagrams for the amplitudes involving Higgs boson and chargino states
as well as those involving fermion and sfermion states. A survey of
supersymmetric parameter space shows that numerous models would be observable
at the $3\sigma$ level with an air Cerenkov telescope with an exposure of $10^4
\meter^2 \yr$.
