The efficacy and safety of intravenous tocainide were compared with intravenous lidocaine in patients with chronic ventricular arrhythmias in a double-blind, parallel study. Twenty-nine patients were randomized to a tocainide (n = 15) or lidocaine (n = 14) group. Antiarrhythmic efficacy was defined as a greater than or equal to 50% reduction in single ventricular premature complex (VPC) frequency, greater than or equal to 90% reduction in paired VPC frequency, and total abolition of ventricular tachycardia. Efficacy was observed in 40% (6 of 15) of patients in the tocainide group and in 36% (5 of 14) patients in the lidocaine group. A 75% or greater reduction in total VPCs occurred in 40% (6 of 15) of patients in the tocainide group and in 57% (8 of 14) of patients in the lidocaine group. Greater than 90% suppression of paired VPCs occurred in 9 of 13 (69%) patients taking tocainide and in 6 of 11 (54%) patients taking lidocaine. Total abolition of ventricular tachycardia was documented in 5 of 11 (45%) patients given tocainide and in two of six (33%) patients given lidocaine. A total of 17 adverse reactions affecting 86% (12 of 14) of patients taking lidocaine and 11 adverse reactions affecting 53% (8 of 15) of patients taking tocainide occurred. Four patients in each treatment group suffered dose-limiting adverse effects. This study suggests that the efficacy and safety of intravenous tocainide are similar to that of intravenous lidocaine in patients with chronic ventricular arrhythmias.