Causes of exit temperature nonuniformity in the primary combustion system of the F100 augmented turbofan engine have been identified and investigated in a comprehensive test program. This test program involved a combination of instrumented full engine, annular combustor rig, and subscale component rig tests. Modifications to the fuel nozzle, which provide significant improvements in combustor exit temperature uniformity, are now being incorporated into the production version of the engine. Modifications to the combustor configuration are being incorporated into growth versions of the engine.