Process for producing asymmetrical hollow filament membranes of polyamide

A process is disclosed for the production of asymmetrical hollow filament membranes suitable for ultrafiltration and/or microfiltration, in which a spinning solution composed of a polyamide or a mixture of polyamides and/or copolyamides, formic acid and a coagulating core liquid, is extruded into a coagulating setting bath liquid, and the hollow filaments are stretched after leaving the setting bath, in the wet state. The pH-value-difference between core liquid and setting bath liquid should be at least 3. The spinning solution contains, in particular, 15 to 25% by weight polyamide, 5 to 20% by weight polyethylene glycol, up to 10% by weight customary additive and formic acid. Preferred embodiments include a stretching ratio amounting to between 1:1.5 and 1:2.5, and having core liquid and setting bath liquid chosen from various combinations of caustic soda, glycol, formic acid or polyethylene glycol. Also disclosed are hollow filament membranes in which the hollow filament is of uniform, eccentric or profiled shape.