The authors have used the SAS-2 gamma -ray data and the Lick survey galaxy count data to determine the functional relationships between the absolute gamma -ray luminosities L_y and the absolute optical or X-ray luminosities of different classes of extragalactic objects such as quasars, Seyfert galaxies and X-ray clusters. From these, the authors are able to derive their contribution to the extragalactic gamma -ray background. They have shown that quasars (B<20) and Seyfert (type 1 and 1.5) galaxies together contribute to a substantial part (59_-26⁺⁵⁵%) of the diffuse gamma -ray background in the 35-100 MeV range, while X-ray clusters are negligible contributors. Therefore they conclude that the extragalactic gamma -ray background is likely to be generated by active galaxies such as quasars and Seyfert galaxies.