Abstract 1. 1. After equilibration for 2 hr in Ringer's solution containing Na 22, frog retinas were transferred to a chamber through which fresh Ringer's solution flowed and aliquots collected and analyzed for Na 22. A high Na 22 concentration was obtained in the first aliquot, followed by low concentrations in succeeding aliquots. 2. 2. A small increase in Na 22 leaving the retina after 4–10 min in the flow chamber, followed by a decrease, was usually observed. 3. 3. After transferring the retina to a series of tubes in which there was no flowing solution, the Na 22 leaving the retina always greatly increased. 4. 4. Different methods of tranferring the retina from the following solution did not affect the results. 5. 5. Removing the retina temporarily from the flowing solution, or temporarily stopping the flow of solution, increased the Na 22 leaving the retina. 6. 6. It is suggested that the flow of solution inhibits retinal sodium diffusion.