Within the scope of the study of the heteroionic exchange in the bone mineral, the sodium-to-calcium ratio was established in femora of 55 male ICR mice. The purpose of the work was to establish the precision of the method as well as biological variations, since the authors intend to investigate the sodium-to-calcium ratio on pathophysiological models in the future with a special regard to osteoporosis. The resulting mean value was of 0.02515±0.00053. The small standard deviation indicates that the ratio is not subject to considerable individual variations. The accuracy of the method was checked by analyzing the reference bone sample IAEA H-5. The results obtained exerted a good agreement with the certified sodium and calcium concentrations.