The long-term anti-arrhythmic efficacy of lorcainide (R15 889) was studied in 20 ambulatory postmyocardial infarction patients. Lorcainide reduced the frequency of ventricular ectopic beats by more than 70% and 90% in 17 and 11 of the patients respectively. The anti-arrhythmic response improved with long-term administration of the drug. Fourteen patients complained of insomnia during the early stages of the study, but this side-effect waned later on. On electrocardiographic examination, the P-R interval, QTc interval and QRS duration were prolonged, and T-wave changes were noted while the patients were receiving lorcainide. Lorcainide seems to be a useful addition to the available anti-arrhythmic agents, and should form part of the armamentarium against ventricular ectopic activity.