Clopidogrel is a new antiplatelet prescribed for the secondary prevention of atherosclerotic events. The literature shows that the clinical manifestations of clopidogrel hypersensitivity include urticaria1, skin rash2-4, and angioedema5. The precise immunological mechanism underlying clopidogrel hypersensitivity has not been established. We describe two cases of hypersensitivity reaction due to clopidogrel. The first constituted an immediate reaction after clopidogrel intake. In this case we demonstrated type 1 hypersensitivity using cutaneous tests. The second case represented a delayed hypersensitivity reaction confirmed by oral challenge testing, in which good tolerance to other antiplatelet drugs such as ticlopidine was demonstrated.