Oral sotalol was given to 64 patients (78% postinfarction) with recurrent, reentrant ventricular tachycardia (VT) during an average follow-up period of 19.7 months. Fifty-nine (92%) patients had previously experienced recurrent ventricular tachycardia, in spite of having received an average of three conventional antiarrhythmic drugs (13 had previously failed on other Class III drugs). The nature and mechanism of the VT was proved with electrophysiologic testing (EPS), and the chronic sotalol dosage was determined by repeated EPS at 3- to 4-day intervals until the VT was no longer inducible. Sotalol failed in five patients and was discontinued in six patients because of severe side effects (three proarrhythmic effects, including two with torsades de pointes)--a total of 18%. Sotalol was successful alone in 42 patients (65%) and in combination with another antiarrhythmic drug in 11 patients (18%). The average dose of sotalol required for success was 589 mg; 658 mg was the mean daily dose when given alone and 486 mg when given in combination. Side effects were common and were due mainly to the beta-blocking effects of sotalol. Dual chamber pacing was required by 11 patients because of poorly tolerated bradycardia, and 14 patients remained symptomatic from worsening of the cardiac failure in spite of pacing, increased diuretics, or vasodilator therapy. The average drug dosage was the same for symptomatic (680 mg) and asymptomatic (627 mg) patients. Sotalol is a valuable antiarrhythmic drug for reentrant ventricular tachycardia. High doses are needed, and at these doses the beta-blocking activity is responsible for most of the side effects.