This article reviews our knowledge about the efficacy of Class I antiarrhythmic agents, especially quinidine, propafenone, and flecainide, for pharmacologic conversion of atrial fibrillation to sinus rhythm. When given intravenously or orally for the long term, conversion rates between 50% and 90% are reported for restoration of sinus rhythm as well as for maintenance of sinus rhythm after DC cardioversion. Based on transtelephonic monitoring of arrhythmia recurrences as well as tolerance, Class IC agents appear to be especially effective for suppressing clinical symptoms in patients with paroxysmal atrial fibrillation. For patients who develop atrial fibrillation following coronary artery surgery, Class I agents are the second choice of treatment only. The concept of single oral loading with Class IC agents for conversion of atrial fibrillation appears attractive, but more data are needed before we conclude that it is efficacious as well as safe when given to ambulatory patients. Because all Class I antiarrhythmic agents have the potential for lethal proarrhythmia, the greatest and as yet unsettled issue is safety. Until the advent of large-scale and long-term trials demonstrating the efficacy and safety of Class I agents for the treatment of patients with atrial fibrillation, this strategy, although very popular to suppress frequent and unpleasant symptoms due to atrial fibrillation, cannot be regarded as firmly established.