To examine the clinical significance of ST-T isopotential maps, 87-lead body surface mapping was performed after treadmill exercise in 21 patients with effort angina pectoris, single-vessel disease, and normal ST-T waves on the resting electrocardiogram. Single-vessel disease was found in the left anterior descending artery (LAD) (nine patients), in the right coronary artery (RCA) (seven patients), and in the left circumflex artery (LCx) (five patients). At 40 msec after the J point, the isopotential maps showed the site of the minimum to be in the left anterior chest in all patients. According to the changes in the position of the minimum from the ST segment to the T wave, postexercise maps were classified into four types. Type A maps (n = 8) were characterized by the persistence of the minimum in the left anterior chest until its negativity decreased and until it became less negative than another minimum that subsequently appeared in a different position. Type B maps (n = 6) were characterized by the gradual movement of the minimum toward the lower thoracic surface. Type C maps (n = 5) were characterized by the gradual movement of the minimum to the left upper direction and then to the back. Type D maps (n = 2) did not show any of the characteristics of A, B, or C. All patients with type A, type B, or type C maps had single-vessel disease of LAD, RCA, or LCx, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)