The absorption of potassium ions by cells of red beetroot tissue plasmolysed in various media has been examined and compared with that of unplasmolysed cells under similar experimental conditions. It is established that although the plasmolysing agents in themselves tend to promote the absorption of ions at the concentrations employed, the effect of plasmolysis is to inhibit the rate of potassium uptake. Evidence is provided that this is due to an increase in the rate of leakage of ions from plasmolysed cells, and to a reduction of gross uptake. These results are discussed in terms of the structural and physiological changes which are associated with plasmolysis. It is concluded that alterations in the surface area, and thickness or density of the protoplasts, modifications of the vacuolar concentration of ions, and respiratory influences are all involved. Another factor, the nature of which has not been elucidated, also appears to be involved.