The diagnosis of acute myocardial infarction (AMI) in the elderly is difficult and often depends on the results of investigations. In a 3-month prospective study, 270 patients admitted to an acute geriatric unit were studied to determine the most effective diagnostic strategy for the diagnosis of AMI, and to assess the value of screening acute geriatric admissions for AMI. Patients were assessed clinically and investigated with serial electrocardiograms and measurements of serum creatine kinase (CK), aspartate aminotransferase (AST), and lactate dehydrogenase activities on three consecutive days after admission. Measurement of serum activity of CK and AST had a diagnostic sensitivity of 100% and specificity of 86.8% for AMI. This was the optimum combination of cardiac enzymes in the diagnosis of AMI. Although electrocardiograms on the first two days of admission had a low diagnostic sensitivity (33.3%) their usefulness was their high positive predictive value (100%) when characteristic of an AMI. AMI was considered in the differential diagnosis of 79 patients (29%). All 25 patients (9%) who had an AMI were in this group, and therefore screening all geriatric admissions for AMI is not clinically justified.