In this report, description of the first stage of some work on the dynamic loading of gear teeth is given. The work has been performed on a power circulating gear rig, using gears of 9 inch P. C. D., 4 D.P., and 1/2 inch face width. The rig is capable of running at pitch line velocities up to 20,000 ft/min. with imposed leads of up to 3,000 lbs/ inch of face width. Particular reference is made to the instrumentation problems which were encountered, and to the measurement of the shape of the gears and their associated transmission errors. No attempt is made at a theoretical analysis of the results obtained as this will be the subject of a future report, along with the publication of more results.