We propose a systematic study of the Infrared properties of Blazars
(BL Lacertae objects and flat radio spectrum quasars) detected at
high (>100MeV) energies by the EGRET instrument on board the Compton
Gamma Ray Observatory (CGRO). By exploiting the full wavelength range
available to ISO, we intend to measure the continuum spectral energy
distribution out to 200 microns and test those models wherein the high
energy gamma rays are produced by Inverse Compton scattering of IR
photons. Ultimately we will combine this study with (ISO) archival
investigations of the IR properties of AGN which have NOT been shown to
be luminous gamma ray sources by CGRO, and search for systematic
differences between the two samples.