We report the case of a patient who presented with a clinical picture of serum sickness with some characteristics of anaphylactoid purpura (Henoch-Schonlein purpura) five days after receiving streptokinase as a treatment for myocardial infarction. The appearance of Henoch-Schonlein like vasculitis after streptokinase treatment was particularly intriguing in view of the common association of streptococcus infection with this type of vasculitis. The production of streptokinase specific IgG and IgA antibodies was studied in the patient and compared with six controls treated with identical doses of streptokinase without adverse effects. A more rapid increase of streptokinase specific IgA was detected in the patient, with a significant higher amount of streptokinase specific IgA and IgG after six days of treatment. These results suggest that different kinetics could induce a precipitation of the immune complexes responsible for vasculitis. However, we cannot exclude that the IgA found in the vessel walls was only an "innocent bystander" deposited as a secondary event.