We present a new method for determining the low-energy stopping power of H and He in solids. The yield vs. energy for the nuclear reaction 3He + 2H → 4He + 1H1 is strongly dependent on the energy of the incident ion which may be either 3He or 2H. This yield can be used to monitor the energy loss in thin films which are evaporated over part of a substrate into which has been incorporated either 3He or 2H. The energy loss is determined by comparing the yield from the film covered and the uncovered part of the substrate. This method should yield accurate stopping powers for 2H from 60-270 keV, and for 3He from 80-360 keV. Film thicknesses of the order of 450-800 Å can be used, minimizing some uniformity problems. Stopping powers of 2H are presented illustrating the technique. © 1978.