AbstractThe subcutaneous injection of solutions of chloride salts of the rare earths is follwed by calcification of the dorsal fascia in the mouse. The concentration of salt required to produce a constant, predictale response varies from salt to salt. The macroscopic outline of the reaction is generally irregular and therefore a quantitative radiological method has been developed to allow an accurate assessment of the dose/response relationship. This with the majority of salts is best described as a log regression and with three as a linear regression.