A terminal r wave in Lead V1 lower than 0.6 mV. was studied in the ECGs of four groups: (1) 104 healthy children, (2) 207 healthy young adults, (3) 171 patients with no autopsy evidence of a cardiopulmonary disease, and (4) 1,078 autopsy patients with a cardiopulmonary disease. Cases with a complete right bundle branch block were excluded. A terminal r wave occurred in 2.9 per cent healthy children, 1.4 per cent of healthy young adults, 0.6 per cent of patients without and in 5.9 per cent of patients with autopsy evidence of a cardiopulmonary disease. The occurrence of a terminal r wave was most common in pulmonary patients (10 per cent). But it was also found in patients with an anterior or a posterior myocardial infarction and in some cases of left ventricular hypertrophy. In the autopsy series RVH occurred in 57 per cent of patients with a Qr pattern, in 30 per cent of patients with a terminal r wave higher than the initial one, and in none of the patients with a terminal r wave lower than the initial one. It is concluded that the height of the terminal r wave has clinical significance. A terminal r wave higher than the initial one in Lead V1 is associated with a cardiopulmonary disease in subjects over 30 years of age, while an r wave lower than the initial one seems to be an innocent finding.