An advanced noninvasive signal averaging technique was used to detect late potentials in two groups of patients: Group A (24 patients) with coronary artery disease (CAD) and without sustained ventricular tachycardia (VT) and Group B (8 patients) with CAD and sustained VT. Recorded analog data were digitized and aligned using a cross correlation function with fast Fourier transform schema, averaged and bandpass filtered between 60 and 200 Hz with a nonrecursive digital filter. Averaged filtered waveforms are analyzed by computer program for three parameters: (1) filtered QRS (fQRS) duration; (2) interval between the R wave peak and the end of fQRS (R-LP), and (3) RMS value of last 40 ms of fQRS (RMS). Significant change was found between Groups A and B in fQRS (101 plus or minus 13 ms vs. 123 plus or minus 15 ms, p less than 0. 0005) and in R-LP (52 plus or minus 11 ms vs. 71 plus or minus 18 ms, p less than 0. 002). It is concluded that (1) the use of a cross correlation triggering method and nonrecursive digital filter enables a reliable recording of late potentials from the body surface, and (2) fQRS and R-LP durations are sensitive indicators of CAD patients susceptible to VT.