Method for producing a porous monolayer polymer membrane, which comprises the following steps: (A) providing a membrane-forming casting solution which comprises a membrane-forming polymer and a solvent therefor; (B) providing a non-membrane-forming and nonprecipitating protective solution; (C) providing a support; (D) applying at least the casting solution and the protective solution to the support to form a film comprising a casting solution layer and a protective solution layer bordering thereon; (E) contacting the film with a precipitant; and (F) removing the protective solution layer, wherein in step (D) the film is formed by applying the casting solution to the support to form the casting solution layer, and applying the protective solution to the casting solution layer to form the protective solution layer, or applying the protective solution to the support to form the protective solution layer, and applying the casting solution to the protective solution layer to form the casting solution layer, and subsequently applying a further protective solution to the casting solution layer to form a further protective solution layer, and wherein the protective solution comprises 2-pyrrolidone or a polymer not capable of forming a membrane (surrogate polymer), selected from the group consisting of polyvinylpyrrolidone, polyethylene glycol, polysaccharides and/or polyvinyl alcohol, and a solvent therefor. (A) providing a membrane-forming casting solution which comprises a membrane-forming polymer and a solvent therefor; (B) providing a non-membrane-forming and nonprecipitating protective solution; (C) providing a support; (D) applying at least the casting solution and the protective solution to the support to form a film comprising a casting solution layer and a protective solution layer bordering thereon; (E) contacting the film with a precipitant; and (F) removing the protective solution layer, wherein in step (D) the film is formed by applying the casting solution to the support to form the casting solution layer, and applying the protective solution to the casting solution layer to form the protective solution layer, or applying the protective solution to the support to form the protective solution layer, and applying the casting solution to the protective solution layer to form the casting solution layer, and subsequently applying a further protective solution to the casting solution layer to form a further protective solution layer, and applying the casting solution to the support to form the casting solution layer, and applying the protective solution to the casting solution layer to form the protective solution layer, or applying the protective solution to the support to form the protective solution layer, and applying the casting solution to the protective solution layer to form the casting solution layer, and subsequently applying a further protective solution to the casting solution layer to form a further protective solution layer, wherein the protective solution comprises 2-pyrrolidone or a polymer not capable of forming a membrane (surrogate polymer), selected from the group consisting of polyvinylpyrrolidone, polyethylene glycol, polysaccharides and/or polyvinyl alcohol, and a solvent therefor. <EOS>