synopsisThe well-known interaction between Congo Red and poly(viny1 alcohol), PVA, was studied by equilibrium dialysis. The diffusion of Congo Red into PVA membranes was much more rapid in 0.1N NaCl solution than in water. The dye appeared to be practically immobilized by the membranes in both solvents. A short survey of the dialytic behavior of various classes of ionic dyes through PVA membranes with water as solvent was undertaken. Anionic dyes permeated the membranes only very slowly, whereas cationic dyes permeated the membranes relatively rapidly and dyed them considerably. The existence of negative charges on the PVA membranes was demonstrated by performing dialysis experiments with the anionic dye Orange I1 and the cationic dye Acridine Orange in water and in excess electrolyte (1N NaCl).