The Authors have studied th haemodynamic response of ten normal subjects to the intravenous administration of 160 MRC.U. of Calcitonin in 60 min, by serial measurement of the systolic time intervals. The analysis of results pointed out a minor inotropic effect starting from the 10th minute from the beginning of the infusion. Little but significant decrements (P less than 0.01) in the duration of the pre-ejection phase of the isovolumetric contraction time, as well as a significant increase (P less than 0.01) in the LVET/PEP ratio, have been noted. A negative chronotropic effect (P less than 0.05) has been noted starting from the 30th minute. The mechanism by which Calcitonin can modify the myocardial inotropism in the normal subject is till now unknown, and it could be related to the interference of this hormore on the endocellular movements of Calcium, and on the cellular levels of cyclic AMP.