The proportion of patients with an acute myocardial infarction (MI) whose diagnosis was missed on admission was accessed. The admitting consultants were then tested to see if they could diagnose the patients correctly when they were shown the admission histories and electrocardiograms (ECGs). Twenty-six per cent of patients with a final diagnosis of MI were not correctly diagnosed on admission. Fifty-one per cent of all patients did not receive thrombolytic therapy (TT) mainly because the diagnosis was not made on admission. A smaller proportion of these patients were admitted to the coronary care unit (CCU). The consultants only correctly diagnosed an average of 7.3 of the 20 patients who were mis-diagnosed on admission and would have prescribed TT to an average of 4.3 of these 20 patients. A significant proportion of patients had a diagnosis of MI missed on admission and therefore did not receive TT. Therefore, another aid to diagnosis such as serum creatinine phosphokinase (CPK) measurement should be available as an emergency test.