The aetiology and pathology, as well as the clinical characteristics of those diseases of the nervous system in which the myelin sheaths and the axis cylinders are unsystematically affected, but the other elements of the nervous tissue spared, are as yet incompletely understood. Of these diseases, the group in which the changes of the nervous system are associated with anaemia and other dyscrasias of the haemopoietic system, generally classified as subacute combined degeneration of the spinal cord, is the most clearly defined. However, even in this group cases occur in which the characteristic degeneration of the spinal cord is not accompanied by gross pathological changes in the blood. There is still, therefore, much research required before these atypical cases can be brought into line with the general pathological conceptions of the subacute combined degeneration. Furthermore, the existence and character of pathological changes in the brain and other parts of the nervous system of cases with subacute combined degeneration, apart from the spinal cord, remain to be investigated more fully. The case which we have to report has various special features, the study of which should contribute in some degree to the elucidation of these complex problems. In this case, which presented the typical picture of a subacute combined degeneration without blood changes, there was an extensive affection of the brain and the peripheral nervous system.