Twenty-six patients with Wolff-Parkinson-White (WPW) syndrome were studied by echocardiography. They were classified into the following WPW types: anterior right ventricular pre-excitation (Type I) - six patients; posterior right ventricular pre-excitation (Type II) - six patients; posterior left ventricular pre-excitation (Type III) - fourteen patients. Twenty-three patients were in WPW at the time of study. Four patients with Type I WPW had abnormal systolic motion of the interventricular septum: three paradoxical and one flat. Patients with Type II and Type III WPW had no septal motion abnormalities related to pre-excitation. Three patients had intermittent WPW, Type III; in all three only minor changes in normal septal motion were apparent on WPW beats. Associated cardiac abnormalities were evident in six patients: two mitral prolapse (one Type II WPS and one Tpe III); one idiopathic hypertrophic subaortic stenosis (Type III); one congestive cardiomyopathy (Type III); one hypertrophic nonobstructive cardiomyopathy (Type I); and one atrial septal defect (Type II). We conclude that abnormal interventricular septal motion may occur with Type I WPW abnormality. Other abnormalities are detectable by echocardiography in a high proportion of WPW patients, but do not appear to be associated with any single Wolff-Parkinson-White type.