A double-blind study comparing verapamil with placebo was conducted in 16 Danish departments of internal medicine with coronary care units (CCU). All patients under 75 years of age admitted to the CCU with a suspicion of acute myocardial infarction (AMI) were evaluated. Of 7415 patients, 3917 were excluded on admission because of heart failure, heart block, other severely disabling diseases, or treatment with beta-blockers or calcium-antagonists. Treatment was started on 3498 patients with 0.1 mg kg-1 verapamil i.v. and 120 mg perorally on admission followed by 120 mg t.i.d., or matched placebo. Treatment was continued for 6 months for patients ascertained to have had an AMI according to all three WHO criteria. Treatment was stopped in patients in whom these criteria were not fulfilled. Of 1436 patients with AMI, 717 were treated with verapamil and 719 with placebo. After six months, 92 patients (12.8%) in the verapamil group and 100 patients (13.9%) in the placebo group were dead (NS). After 12 months the mortality rates were 15.2% and 16.4%, respectively (NS). By six months after entry a total of 56 reinfarctions were recorded in 50 patients (7%) in the verapamil group and 66 reinfarctions in 60 patients (8.3%) in the placebo group (NS).