The significance of the Wilson variety of right bundle-branch block was investigated on the basis of serial electrocardiographic changes seen in almost half of the series. Wilson block may originate from both anteroseptal and posterior infarction; in the former it may form a solitary relic without prognostic significance; in the latter it denotes extensive septal involvement. It may modify the injury pattern of anterior infarction and may abolish the signs of posterior infarction; cardiac infarction may approximate it to the classic form of right bundle-branch block. Except in two patients, less than 4 per cent of the series, it was related to pathologic causes; it should therefore be regarded as a sign of organic heart disease.