1. Measurements of visual purple regeneration in solution have been made by a procedure which minimized distortion of the results by other color changes so that density changes caused by the regenerating substance alone are obtained.
2. Bleaching a visual purple solution with blue and violet light causes a greater subsequent regeneration than does an equivalent bleaching with light which lacks blue and violet. This is due to a photosensitive substance which has a gradually increasing effective absorption toward the shorter wavelengths. It is uncertain whether this substance is a product of visual purple bleaching or is present in the solution before illumination.
3. The regeneration of visual purple measured at 560 mµ is maximal at about pH 6.7 and decreases markedly at more acid and more alkaline pH's.
4. The absorption spectrum of the regenerating material shows only a concentration change during the course of regeneration, but has a higher absorption at the shorter wavelengths than has visual purple before illumination.
5. Visual purple extractions made at various temperatures show no significant difference in per cent of regeneration.
6. The kinetics of regeneration is usually that of a first order process. Successive regenerations in the same solution have the same velocity constant but form smaller total amounts of regenerated substance.
7. In vivo, the frog retina shows no additional oxygen consumption while visual purple is regenerating.