A new method for calculating the accretion rate of bone calcium and some observations on the suitability of strontium-85 as a tracer for bone calcium.

1. A new method for calculating the accretion rate (A) of bone calcium is proposed, based on an impulse analysis of 47Ca data. The method is free of most of the assumptions inherent in previous methods of analysis and appears to give more accurate estimates. 2. In fourteen normal subjects and twelve patients with metabolic bone disease, measurements of A by the new method gave very similar results to the mineralization rate calculated by the method of Burkinshaw et al. (1969). Analysis of twelve studies performed by Neer et al. (1967) gave good agreement with their five compartment model. A close relation between A and Marshall's (1964) A5 was observed, but the latter gave systematically higher results. 3. In sixteen studies both 47Ca and 85Sr were injected simultaneously. Although there were no systematic differences between the values of A for the two tracers, the differences between individual values were greater than the known experimental errors.