A double-blind study comparing verapamil with placebo was conducted in 16 Danish departments of internal medicine with coronary care units (CCU). All patients below 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-adrenoceptor blockers or calcium antagonists. Treatment was started in 3498 patients with 0.1 mg kg-1 verapamil i.v. and 120 mg orally on admission followed by 120 mg three times daily, or matched placebo. Treatment was continued for 6 months for patients verified to have had an AMI according to all three WHO criteria. Treatment was stopped in patients for whom the diagnosis of AMI was ruled out. Of 1436 patients with AMI, 717 were treated with verapamil and 719 with placebo. After 6 months, 92 patients (12.8%) in the verapamil group and 100 patients (13.9%) in the placebo group were dead (NS). Fifty patients (7%) in the verapamil group and 60 patients (8.3%) in the placebo group had reinfarctions (NS). After 12 months, 109 patients (15.2%) in the verapamil group and 118 patients (16.4%) in the placebo group were dead (NS). It is concluded that verapamil treatment used in the early phase of an AMI does not improve survival. Based on the experience from the first study we are at present performing a further secondary prevention study with verapamil to a modified design.