1. In drawing the polarographic curve of SH-wave by making arsenic acid at various concentrations act on cysteine and glutathione, because the SH-wave and arsenic wave overlap with one another, it has been impossible to pursue the changes in the amplitude of the SH-wave itself. 2. In drawing the polarographic curve of arsenic wave by making cysteine or glutathione at various concentrations act on arsenic acid solution, no fall in the amplitude of arsenic wave can be recognized. 3. In the investigation of the binding of the SH-group of cysteine, glutathione and BAL with arsenic by Kajita's photometric method, while cysteine and glutathione do not combine with arsenic, the binding of arsenic and a dithiol compound, BAL, has been recognized.