In spite of the many investigations regarding the elimination of the several dyes from the blood from the kidneys, since Heidenhain, there is as far as I know still a lack of systhematic investigation in relation to the diffusibity of dyes. Hoping to fill up this gap I made the following experiments on toads (Bufo japonicus).Method.For my purpose I used the following dyes; Phenol-sulphone phthalein, picric acid, chrysoidin, bismarckbrown, auranin, pyronin, eosin, methylen blue, safranin, patent blue V., rhodamin, extra B., methylviolet, fuchsin, neutralred, alkali blue, indulin, kongored, indigocarmin, carmin extra B,. As a preminary experiment I measured the rate of diffusion of these dyes on the gelatin and agar. The following list is arranged in the descending order of the diffusion rate of the dyes.1. phenol-sulphone phtalein, 2. picric acid, 3. rhodamin, 4. patent blue V., 5. chrysoidin, 6. pyronin, 7. safranin, 8. eosin, 9. fuchsin, 10. bismarckbrown, 11. methylen blue, 12. methylviolet B., 13. carmin, 14. neutralred, 15. kongored, 16. alkaliblue, 17. indulin. Summary. 1) 1. picric acid, 2. phenol-sulphone phthalein, 3. rhodamin, 4. patent blue V., 5. chrysoidin, 6. pyronin, 7. safranin, 8. eosin, 9. fuchsin, 10. bismarckblown, 11. methylen blue, 12. methylviolet, 13. carmin,. The above mentioned dyes are very easily eliminaten from the glomerular capsules but from the tubles the elimination is less in amount and the order is the one indicated above. 2) Neutralred, indulin, alkali blue and kongored are eliminated from the glomerular capsules, but not from the tubles. 3) The more elimination of dyes from the tubles abounds the greater is the diffusion. 4) When perfused from the renal portal vein only, the dyes were eliminated in the lumen, but there was either no elimination of water at all or it had been absorbed by the epithelium of the convoluted tubles. 5) The elimination of the dyes from the glomerular capsules is influenced neither by the supply of oxygen in the fluid-flow nor by poisoning with cyanic acid. The elimination of dyes is not always accompanied by oxydation. 6) The elimination of the dyes from the tubles is influenced both by th supply of oxygen in the fluid-flow, and by poisoning with cyanic acid, and elimination of the dyes is accompanied by oxydation. Accordingly, I summarize as follows.The glomerural capsules allow the diffusion into them of all the dyes, which were made use of in the experiments; and regarding the elimination of dyes from the tubles there can hardly be found an explanation in terms of physical chemistory.