Electrocardiograms obtained serially from 544 patients with non-Q wave infarction in the Diltiazem Reinfarction Study were analysed to compare the short term (less than or equal to 14 days) and long term (one year) follow up of 105 patients (19%) whose admission electrocardiogram showed no localisable repolarisation abnormalities (group 1) with the outcome in 439 patients (81%) who had ST-T wave abnormalities (group 2) localised to two or more contiguous leads within an anterior, inferior, or lateral lead group. There were no major between group differences in baseline clinical variables, concomitant medications, or treatment allocation (diltiazem v placebo). Group 2 patients, in the first year, had a higher incidence of early recurrent ischaemia (angina greater than or equal to 24 hours after myocardial infarction associated with ischaemic repolarisation changes), reinfarction, and readmission for chest pain than group 1 patients, despite comparable creatine kinase and creatine kinase MB activities in both groups. About 20% of patients with acute non-Q wave myocardial infarction did not have definable ST-T wave abnormalities. These patients had a similar clinical and enzymatic profile as patients with non-Q wave infarction with definable ST-T wave abnormalities and they were more likely to have a favourable short term and long term outcome.