During a 3-month follow-up, 131 patients (19.1%) withdrew from blind treatment in both metoprolol- and placebo-treated groups. More metoprolol-treated than placebo-treated patients withdrew because of cardiovascular adverse experience mainly during the very early phase. In all, 45 (6.5%) metoprolol-treated vs 14 (2.0%) placebo-treated patients were not given either a full intravenous dose or a full oral dose 15 minutes later. Bradycardia and hypotension were more common in the metoprolol group, whereas severe atrioventricular block did occur in a similar number of patients in both groups and severe congestive heart failure was more common in the placebo group. Results indicate that tolerance is generally good after intravenous and oral treatment with metoprolol in patients with suspected acute myocardial infarction.