The high efficiency of the BGO detectors makes them a very attractive candidates toreplace NaI(Tl) detectors, which are widely used in studies of body composition. In this work,the response functions of the BGO and NaI(Tl) detectors were determined at 0.662, 4.4, and 10.0MeV using three different Monte Carlo codes; EGS4 1 , MCNP 2 , and PHOTON 3 . These codesdiffer in their input files and transport calculations, and were used to verify the internalconsistency of the set-up and of the input data ...