For measuring the activity of mouse liver rhodanese, the following procedures were found to be most appropriate. After homogenizing the mouse liver, the supernatant layer was employed as the enzyme solution. This solution (1.0 cc) was added with 2.0 cc of 1% NaCN, 0.1 NNa_2S_2O_3,20.0 cc of PH 8.2 phosphate buffer and 30.0 cc of distilled water. It was kept at 38℃ for 2 hours, and deproteinized by trichloracetic acid. After such procedures, the orange color that was brought about by the ferri-reagent was measured by photometer.