We studied the relationship between thrombolysis and late potentials (LP) in 137 patients with acute myocardial infarction (AMI). Among 37 patients treated with tissue-type plasminogen activator(t-PA treated group), LP were recorded in 2 patients (5%). In contrast, among 100 conventionally treated patients (control group), LP were seen in 26 (26%, P less than 0.01). When the two groups were matched with respect to age, sex, absence of prior infarction, LVEF, number of abnormal Q waves, ECG score and CAD score, the same incidence of LP was seen, i.e. 6% of the 34 t-PA treated patients had LP as compared with 24% of the 42 conventionally treated patients (P less than 0.05). Angiographic examination following t-PA infusion revealed that the incidence of LP was 0% and 40% in patients with patent and closed infarct-related coronary artery respectively. 1 year follow-up data showed that no deaths occurred in the t-PA treated group, while in the control group. 18 deaths were recorded and 8 of them were classified as sudden death. These observations suggest that patients with AMI treated early with thrombolysis have electrically more stable ventricles due to improvement of ischemia.