Dialysis membrane and method of making

A single or multilayer dialysis membrane, constructed as a flat film, a tubular foil or especially as hollow fibers, the membrane being made of a regenerated cuprammonium cellulose which may be unmodified or partly modified by alkyl, carboxyalkyl or hydroxyalkyl groups, and said membrane being characterized by an ultrafiltration capacity at 37 DEG C. of 7 to 30 ml/hrxm2.mmHg, an average molecular permeability, based upon vitamin B12, of about 3x10-3 to 12x10-3 cm/min, and a water retention value of more than 145%, calculated according to the German Industrial Standard (DIN) 53814. The new membrane is prepared by the known cuprammonium process but with the addition of a finely ground CuO with a maximum particle size of 20 microns to the standard cuprammonium solution. After casting, extruding or spinning this solution into a coagulating bath, e.g. an alkaline coagulating bath, the regenerated and shaped cellulosic film, foil or filament is given an acid treatment, preferably with sulfuric acid, sufficient to substantially remove the solid CuO particles and to provide a significantly higher pore volume content and other favorable properties in the final membrane.