To determine the electrophysiological properties of oral propafenone, 50 patients (39 male and 11 female, aged 31 to 80 years) with sustained ventricular tachycardia or ventricular fibrillation underwent serial electrophysiological drug testing, using propafenone (750 to 900 mg daily) as the anti-arrhythmic regimen of first choice. During baseline study, all patients had inducible sustained ventricular tachyarrhythmias. After oral loading of propafenone, 37 patients (74%) remained inducible whereas 13 were rendered non-inducible. Among the still inducible patients, the mean VT rate decreased from 223 +/- 38 b.min-1 (baseline) to 172 +/- 32 b.min +/- 1 (P less than 0.001). Four patients showed an increase of VT rate during propafenone compared to the VT rate at control. Non-inducible patients were discharged on propafenone. During a mean follow-up period of 20 +/- 15 months, there were three non-fatal VT recurrences among the responders, two of them due to non-compliance. Thus, propafenone used as the anti-arrhythmic agent of first choice among patients undergoing serial electrophysiological drug testing for ventricular tachyarrhythmias proved effective in suppressing VT induction in 26%. With regard to arrhythmic events, these patients have a favourable outcome.