The use of tissue plasminogen activator (t-PA) in the management of acute myocardial infarction, as effective thrombolytic agent, is well established. Thrombolytic therapy, limiting the extent of myocardial necrosis, reduces the infarct-related morbidity and mortality and improves the prognosis in patients with acute myocardial infarction. Thrombolytic agents present various side effects. Allergic reactions may occur with both streptokinase (ST) (or with anistreplase, the equimolecular mixture of streptokinase and human plasminogen); and t-PA. The incidence of allergic reactions associated with the use of t-PA is much lower if compared with other thrombolytic agents. Since t-PA is structurally identical to endogenous t-PA, its administration should not cause anaphylactic reactions. The purpose of this case presentation is to describe the occurrence of an anaphylactoid reaction during infusion of t-PA in a 63 year-old man, admitted to the Cardiac Care Unit (C.C.U.) with diagnosis of acute myocardial infarction.