Abstract: In a method for the manufacture of a porous membrane by the steps of causing a polymer solution to flow and spread in a uniform thickness on a substrate and solidifying the formed layer of the polymer solution in a bad solvent, the improvement which comprises using a fluorinated hydrocarbon as the bad solvent and optionally carrying out the removal of a good solvent mingling into the fluorinated hydrocarbon during the course of the solidification by the technique of extraction from water, and repeating the fluorinated hydrocarbon.