The incidence of myocardial contusion in patients wearing seat belts and requiring admission to hospital after road traffic accidents was examined. The criteria used for diagnosing contusion were serial electrocardiograms (ECGs) and estimation of CK-MB isoenzymes using the Isomune-CK (Roche) kit. Nine of the 14 patients (64 per cent) showed evidence of myocardial contusion. We suggest long-term studies to establish the true incidence among patients wearing seat belts.