Drivers involved in automobile accidents were screened for the presence of occult cardiac injury without regard for apparent severity of the accident or injury. An electrocardiogram was recorded, and serum levels of total creatine phosphokinase and the MB isoenzyme of creatine phosphokinase (myocardial form) were measured as soon as possible after the accident and subsequently during admission (or on the following day in patients treated and discharged from the emergency room). Electrocardiographic abnormalities were observed in 18 of 82 patients but correlated poorly with other evidence of the severity or location of injury. Of the 22 drivers admitted to the hospital (for any cause), nine demonstrated significant early elevations of the activity of the MB isoenzyme of creatine phosphokinase. We conclude that blunt cardiac trauma is a clinical subtlety; to be found, it must be sought. The ECG is of limited value. Measurement of the serum activity of the MB isoenzyme of creatine phosphokinase early after injury would appear to offer the best evidence of cardiac trauma.