The photoneutron thresholds for C12, N14, O16, Cu63, and Ag109 were determined by measurement of the yield of activity as a function of the peak bremsstrahlung energy. Measurements of the photoneutron thresholds of C12, N14, and O16, which could be calculated accurately from the mass data, served to determine the energy scale. The photoneutron thresholds for Cu63 and Ag109 were found to be 10.61+/-0.05 Mev and 9.07+/-0.07 Mev, respectively. The shape of the activation curves for C12, N14, and O16 appeared to be a straight line for about 350 kev near threshold. The activation curves for Cu63 and Ag109 could be fitted accurately by functions of the form Y=k(E-Et)2.23 and Y=k(E-Et)1.90, respectively, over a 3-Mev interval. E refers to the peak x-ray energy and Et to the threshold energy.