Echocardiograms of 52 patients with the Wolff-Parkinson-White (WPW) syndrome were investigated. Abnormal patterns of motion were observed in the left ventricular posterior wall (LVPW) and the interventricular septum (IVS). The abnormal LVPW motion was presumably specific for the syndrome and included early onset of the anterior motion which preceded the first heart sound (S1) and a premature peak formation of the anterior displacement which occurred before the second heart sound. The latter was usually followed by a second lower peak. These findings seem to suggest that both contraction and relaxation of LVPW begin earlier than normal due to ventricular pre-excitation initiated at or near the LVPW. The IVS abnormality characteristic of the syndrome was a posterior protrusion, the onset of which preceded S1. Subsequent motion of IVS was either paradoxical or hypokinetic during ejection. These IVS abnormalities were quite similar to those observed in left bundle branch block. The abnormal LVPW motion was observed in all 20 Type A patients and 10 of the 32 Type B patients. The abnormal IVS motion was observed in 10 Type B patients. We feel that echocardiography could be used as an auxiliary noninvasive means of locating the pre-excitation site in patients with WPW.