A case of serum sickness was observed 7 days after administration of intravenous streptokinase in the acute phase of myocardial infarction. The clinical presentation was the sudden development of fever, a papuloerythematous skin rash, myalgia and polyarthritis accompanied by a severe biological inflammatory syndrome without any signs of bacterial or viral infection. Spontaneous regression was observed within 72 hours. Although this complication of streptokinase fibrinolysis seems to be rare, clinicians should be aware of it and not confuse the allergic reaction with that of another drug, the withdrawal of which could be prejudicial for the patient.