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We estimate the contribution of radio-loud active galactic nuclei to the γ-ray background using the recent detections by GRO of BLLacs and flat-spectrum radio quasars at energies > 100 MeV. From the recently derived radio luminosity functions of these objects, together with the observed mean alues of the γ-ray to radio luminosity, we derive contributions of about 30 and 35 per cent, respectively, at 100 MeV. The total contribution of radio-loud sources is |66-₂₄^+31| per cent, leaving little room for a substantial contribution from radio-quiet active galactic nuclei, none of which has been detected so far. Our results assume that the detected sources are typical of the radio-loud population and not strongly variable; further γ-ray detections and variability studies should allow a refinement of our estimate.
Padovani et al. (1993) studied this question.