The total stresses in a mating gear pair arise from two sources: 1) externally induced stresses associated with the transmission of power@ and 2) residual stresses associated with the heat treatment and machining of the tooth profiles. The stresses due to power transmission are the result of complex normal and shearing forces that develop during the meshing sequence. The total stress from these two sources contributes to the life of a gear. This paper@ funded by the AGMA Foundation@ presents the results of research directed at measuring the total stress in a pair of statically loaded and carburized spur gears. Measurements were made using neutron diffraction methods to examine the change in total stress as a function of externally applied load and depth below the surface. The paper includes a summary of the various test methods that were used and a discussion of their applicability to carburized gears.