473 patients with suspected acute myocardial infarction were entered into a randomised, double-blind, placebo-controlled comparison of disopyramide phosphate, 150 mg three times a day, and oxprenolol, 40 mg three times a day. When analysed on an intension-to-treat basis there was no significant difference in 6-week mortality between the groups, but patients who were able to continue on the active medications fared better than the patients who had to be withdrawn. The withdrawal rate because of heart failure in patients randomised to receive disopyramide was significantly increased. Patients receiving this agent also showed a reduced number of arrhythmic episodes on 24-h tape recordings but this trend did not achieve statistical significance. The results show that the early use of either oxprenolol or disopyramide phosphate in patients with suspected acute myocardial infarction is unlikely to improve mortality.