1. A study was made of the birefringence of retinal receptors obtained from the retinae of frogs, cats, rabbits and goldfish.2. Normal rods and cones show similar optical activity.3. The effects of fixatives, lipid solvents, de‐ and rehydration, and temperature were examined.4. Rods fixed with formaldehyde preserve normal optical activity for a long time while glutaraldehyde changes it swiftly in a manner similar to that resulting from the application of heat.5. Alcohol acts like a denaturing agent rather than as a solvent for rod lipids.6. The action of glutaraldehyde on goldfish rods is instantaneous but cones preserve their normal activity for up to 1 hr.7. A number of striking parallels between the presence of the R2 component of the early receptor potential (as reported in the literature) and optical activity are listed; it is suggested that normal optical activity is a prerequisite for the recording, if not the elicitation, of R2.