GRANULARITY OF THE DIFFUSE BACKGROUND OBSERVED

First results are reported from a program for measuring the field-to-f ield fluctuation level of the cosmic diffuse background by using diffe rences between the two background positions of each deep exposure with the HEXTE instrument on RXTE. With 8 million live seconds accumulated to date a fluctuation level on the 15-25 keV band is observed which i s consistent with extrapolations from the HEAO-1 measurements. Positiv e results are expected eventually at higher energies. Models of AGN or igin will eventually be constrained by this program.