Since the reported incidence of pericardial effusion following thrombolysis is highly variable, we have evaluated 80 consecutive patients with first acute myocardial infarction treated with streptokinase. Two-dimensional echocardiographic studies were performed on days 1,2,3, and 7, at 3 and 6 weeks, and 3, 6, and 12 months following acute myocardial infarction. Throughout the study, pericardial effusion was found in 7 of 80 (8.75%) patients, being small in 5 patients, moderate in 1 and large in 1 patient. No clinical, angiographic, or echocardiographic variable was associated with pericardial effusion formation. The incidence of pericardial effusion found in our study is almost three times lower than in other echocardiographic studies on pericardial effusion in thrombolysed patients. Whether this differences results from the beneficial effects of streptokinase is not clear.