A study using two methods of noninvasive registration of ventricular late potentials (VLP), computer averaging and beat-to-beat spatial averaging, was conducted in 27 patients with ventricular tachycardia and 11 healthy volunteers. Both techniques are described in detail. The duration of QRS complex on high resolution ECG was found to be significantly longer in patients with VLP as compared to those of patients without VLP and having ventricular tachycardia as well as healthy adults. The data obtained by both methods do not differ significantly. The beat-to-beat method was not informative in about 20% of cases because of the ineffective filtering procedure and the presence of myographic noise on the amplified CS. The duration of VLP was 44 +/- 20 ms in patients with documented ventricular tachycardia. The sensitivity of the assessment of arrhythmogenic ventricular activity was 70% with the computer method, and 59% with the beat-to-beat spatial averaging technique. The specificity and predictive value of both registration methods were 100%.