Minimum yield of backscattered protons and H-atoms with primary energies of 50–150 keV from a well annealed Nb single crystal has been measured in single and double alignment as a function of emerging energy at different temperatures. From these data minimum yield as a function of depth has been calculated, assuming electronic energy losses only. The results are compared to analytical equations for minimum yield in single and double alignment. These equations were obtained from Lindhard's theory of electronic and nuclear multiple scattering in single crystals. It was assumed that transverse energy increases steadily with penetration depth, diffusion being neglibible. At higher energies the agreement between theory and experiment is good in <100> single alignment. In <110> single alignment and at lower energies experimental values are about a factor of 2 higher. In double alignment there is a discrepancy of nearly one order of magnitude, which probably must be attributed to lattice defects.