Cation loading of red blood cells.

1. p-Chloromercuribenzenesulphonate induces an increase in the permeability of red cell membranes to monovalent cations. Under suitable conditions the increase in permeability is large enough to allow cell cation concentration to approach equilibrium with that in the suspending media in 24 hr at 5 degrees C.2. The effect of the mercurial on permeability is fully reversed by cysteine.3. These effects provide the basis for a simple procedure for preparing red blood cells of almost any desired sodium or potassium content.4. If hypertonic media are used, cells can be obtained with normal volume but in osmotic equilibrium with the hypertonic solutions.