Randomized, fixed sample, multicenter trial conducted at 14 institutions. Patients meeting clinical criteria underwent Holter monitoring. Those having an average of 30 premature ventricular contractions per hour underwent EPS. Those having inducible ventricular tachycardia were randomized into an EPS arm or to a Holter exercise treadmill arm of drug testing. Each patient received, in random sequences, up to six antiarrhythmic drugs. When an effective drug was found, patients underwent a predischarge HM and exercise test. Follow-up continued for one year after the last subject had been randomized. The primary endpoint in the trial was time to arrhythmia recurrence during therapy with a drug predicted to be effective by either EPS or HM.