From my investigations of five families subject to Huntington's Chorea, I have come to the following conclusions. 1. Two of them are considered as double phenotypes of chorea and schizophrenia. Others remind us of double phenotypes of ptosis and the so-called lethal factors. 2. Four families are found to be subject to dementia and psychopathia as much as to choreatic movement; one family is liable only to psychopathia. Two families have a tendency to attempt suicide, commit murder and other crimes. 3. A case of anatomical examination shows a remarkable change in the cerebellar cortex, dentatum and nucleus olivalis, in spite of the slight change in striatum and cerebral cortex. Cases of change in nucleus olivaris may perhaps be rare. 4. Such "Disease Gene" as chorea Huntingtoni or "Lethal Factor", I suppose, is caused by the degradation or loss of functions of "Normal Gene" through mutation. Can it not be reasoned, then, that the very existence of "Disease Gene" brings the functions of "Normal Gene" into relief?