The authors report their investigations in ten patients suffering from Sudek's syndrome of the foot, studied by the use of the radioosteotrope 99mTc-Pirophosphate. Through this radioindicator it has been possible to evaluate qualitatively (scintigraphy) as well as quantitatively (scintimetry) the modifications of the metabolism induced by the administration of calcitonin. The evaluation, whose radioisotopic method is described in detail, has been carried out at various intervals during treatment with calcitonin (from two to six months). The normalization of the readjustment of the bone generally corresponded with marked clinical recovery of the patient.