  The attenuation of very high energy gamma rays by pair production on the
Galactic interstellar radiation field has long been thought of as negligible.
However, a new calculation of the interstellar radiation field consistent with
multi-wavelength observations by DIRBE and FIRAS indicates that the energy
density of the Galactic interstellar radiation field is higher, particularly in
the Galactic center, than previously thought. We have made a calculation of the
attenuation of very high energy gamma rays in the Galaxy using this new
interstellar radiation field which takes into account its nonuniform spatial
and angular distributions. We find that the maximum attenuation occurs around
100 TeV at the level of about 25% for sources located at the Galactic center,
and is important for both Galactic and extragalactic sources.
