The invention relates to ion-selective diaphragm/spacer units for dialysis, electrodialysis or electrolysis consisting of an organic polymer modified by anionic or cationic groups and a flat, porous structure consisting of a material functionalized by anionic or cationic groups, said material having a thickness ranging from 10->-2 and 10->-4 m and pore diameters ranging from 10 to 1000 A.