We compared a "cardiac profile" test with standard creatine kinase (CK) and lactic dehydrogenase (LD) electrophoresis in 798 cases of possible acute myocardial infarction (MI). The cardiac profile enzyme screen (CK-B, CK, LD) used on 495 patients who came to the emergency department with chest pain suggestive of acute MI but without diagnostic ECG changes. Instead of admission to the coronary care unit, they were placed on observation status (Chest Pain Evaluation Unit) for a period up to 20 hours (average 11.1 hours). Using the results of the cardiac profile, 327 were able to be sent home. Of the 168 patients admitted, only 30 (18%) had subsequent enzyme evidence of myocardial necrosis. Use of the chest pain evaluation unit resulted in an 80% reduction in cost of ruling out acute MI for the 327 patients not admitted.