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The contribution to the cosmic diffuse gamma-ray background (CGB) from Gamma Ray Bursts (GRBs) is studied in the 40 keV - 2 MeV regime. We use High Energy Resolution (HER) data from the Burst And Transient Source Experiment (BATSE) aboard the Compton Gamma-Ray Observatory (CGRO) to generate a GRB template spectrum. Although the GRB contribution to the CGB is generally small, in comparison to the dominant flux from Type Ia supernovae, the integrated GRB flux is in fact comparable to that from SNIa in the narrow 10-40 keV range. GRBs contribute to the CGB at the same level as Type II supernovae do. Although BATSE data are not available below ~40 keV, extrapolation of the template spectrum suggests that bursts can fill a significant part of the existing gap between Seyfert galaxies (dominating the CGB below ~ 100 keV) and SNIa (dominating at ~1 MeV). We estimate contributions from Cen A-like (FR I) radio galaxies in this energy regime, where INTEGRAL data is expected to provide major advances.