Sudden cardiac death and ischaemic cardiac events occur in a circadian pattern. Because ventricular tachycardia is thought to play an important role in sudden cardiac death, the episodes of spontaneous ventricular tachycardias (greater than 3 consecutive beats) (n = 1314) were analysed from 24-hour long term electrocardiographic recordings in 34 patients with coronary arterial disease to determine whether circadian rhythm exists in spontaneous ventricular tachycardia. Twelve patients had suffered cardiac arrest, four patients had a history of syncope, and palpitation was the indication for electrocardiographic recordings in eighteen patients. Analysis using chronobiologic single cosinor method showed a significant circadian variation in the occurrence of ventricular tachycardia episodes with the peak occurring at 6 a.m. Similar circadian rhythm was also observed in the occurrence of the longest episode of ventricular tachycardia. Ischaemic ST-segment depression preceded the longest ventricular tachycardia episode only in one patient. Thus, a circadian rhythm occurs also in spontaneous episodes of ventricular tachycardia, a finding which is similar to that in sudden cardiac death.