The diagnostic performance of a new enzyme linked immunosorbent assay for the cardiac structural protein troponin T in the differential diagnosis of ischaemic cardiac damage was assessed. A well documented set of patients admitted to the coronary care unit of a district general hospital were studied. At a cutoff value of 0.2 micrograms/L, troponin T measurements 12-24 h after admission or 12-16 to 24-48 h from onset of chest pain showed an overall efficiency of 97.6% for diagnosis of proven myocardial infarction. Troponin T was not detectable in patients when ischaemic heart disease could be excluded but was present in four patients with angina. Detectable troponin T in these angina patients was associated with subsequent cardiac events.