A case of anaphylactic shock determined by intramuscular administration of a dose of synthetic calcitonin in a 64-years-old man is described. The patient had not suffered significant cardiovascular events in the past; he smoked twenty cigarettes a day and he was treated with calcitonin for osteoporosis and polyarthrosis. Allergy to diclofenac was demonstrated in the past while preceding administrations of spray calcification didn't provoke side-effects in the patient. Nevertheless after the second i.m. administration of the drug he suddenly fainted. Dyspnea, severe hypotension and maculo-papular erythema were present at the moment of admission to our hospital. The continuous electrocardiogram monitoring showed a characteristic "migrant" ST elevation at first in the anterior leads, then in inferior and septal leads, and premature ventricular and atrial beats. The echocardiographic transtoracic examination proved an apical and septal akinesia which completely disappeared after one hour at a second echocardiographic examination. In spite of intensive medical treatment (lignocaine and hydrocortisone e.v.) the patient had a sustained ventricular tachycardia that quickly degenerated into ventricular fibrillation. After one DC shock at 300 joules we observed spontaneous spontaneous restoration of the normal sinus rhythm. The following clinical evolution was good and no other arrhythmias or cardiovascular symptoms were observed. In order to estimate the reasons of the clinical picture the patient was submitted to serial blood examinations, serial electrocardiograms, exercise stress test, echodypiridamole stress test and serial echocardiograms. The blood examinations showed a relative eosynophilia (3%), the increase of IgE serum level (316 UI) and transient ipokalemia (2.3 mEq/l). None pathological findings were observed in the other examinations.(ABSTRACT TRUNCATED AT 250 WORDS)