Holter monitoring is the most commonly used noninvasive method for assessing antiarrhythmic drug therapy. It can easily be performed and we know the exact criteria for the definition of drug efficacy and the proarrhythmic effect. However, the value of Holter monitoring to predict clinical outcome in patients with malignant ventricular arrhythmias is controversial. Several authors claim that Holter monitoring is useless to evaluate antiarrhythmic drug effects. Theoretical considerations will explain that it is not the technique by itself that is useless; it is the way it is applied. Merely by changing the efficacy criteria, the value of Holter monitoring to assess antiarrhythmic effects can be improved significantly. Nevertheless, Holter monitoring is far from being the ideal method. It focuses only on arrhythmia density, denying that other risk factors such as heart rate variability, ischemia, and QT changes may be of additional prognostic value. Further studies with Holter monitoring should concentrate on the role of these parameters.