Body surface potential mapping (BSPM) was used to study the spatial distribution of late ventricular potentials. In a group of 15 normals and 21 patients with documented ventricular tachycardia (VT), BSPM performed with 63 averaged and high-pass filtered ECG leads (LP-BSPM) showed that late potentials have a mostly dipolar distribution and that they can be reasonably well detected with only three orthogonal leads. In a group of 17 VT patients who also had BSPM performed during induced VT (VT-BSPM), six patients had LP-BSPM similar to one of the VT-BSPM, suggesting that the locations and orientations of both types of sources are similar. In a group of 12 VT patients who had epi-endo VT mapping at surgery, LP-BSPM showed close extrema (reflecting antero-apical delay) for patients with anterior or apical VT sites, suggesting that VT originates in delayed regions. BSPM thus provides useful information about the detection and significance of late potentials.