(1) This study, performed by Congo red test and electroretinogram, is concerned with the relation between the activity of reticulo-endothelial system and the threshold of b-wave of electroretinogram under normal and under excitatory state of reticulo-endothelial system.(2) The granulopectic activity of reticulo-endothelial system was tested by Congo red test.(3) The activity of reticulo-endothelial system was excited by the injection of a dose of 20 mg. carbon particles per 100g. of body weight. The results of Congo red test obtained under normal state were 35-40%, and that obtained under excitatory state of reticulo-endothelial system (by means of injection of carbon particles) was about 50%.(4) Scotopic sensitivity was calculated as the reciprocal of the threshold ofb-wave, so the lower the threshold intensity, the greater was the scotopic sensitivity, and the greater was the increase of the height of b-wave.(5) After2hours of injection of a suspension of carbon particles, the height of b-wave (elicited by monochromatic stimli of which wave lengths are 400, 430, 500, 520, 550, 580, 610, 640 and 670mμ) was rapidly increased.(6) After the injection of a dose of 20mg. carbon particles per 100g. of body weight the threshold intensities of b-wave are decreased. Initially the threshold remained constant for about two hours. During a period of 2-4 hours after injection they fell rapidly, after which they did decrease no more.(7) Scotopic sensitivity curve has two humps, one is in green region and the other in red. The maximum of the hump in green region is 520mμ, and the maximum of the curve for visual purple absorption is 500mμ. Therefore, the cause of the decrease of threshold of b-wave in green region may be assumed to be the augmentation of regeneration of visual purple. But the cause of the decrease of threshold of b-wave in red region may be assumed to be the augmentation of regeneration of unknown visual pigment of which maximum of absorption curve is 610mμ.