A positive-working radiation-sensitive mixture is described which is composed of a compound having at least one C--O--C bond which can be split by acid, a compound which forms a strong acid when irradiated, a binder which is insoluble in water and soluble in aqueous-alkaline solutions, and a resin having solubility properties which differ from those of the binder and which is selected from (1) a polyurethane resin obtained from an organic isocyanate and a polymer which contains hydroxyl groups, (2) a polyvinyl alkyl ether, (3) an alkyl acrylate polymer, or (4) a hydrogenated or partially hydrogenated derivative of colophony. As a result of the resin additives, photoresist layers are obtained which have good adhesion to the support, good flexibility, good latitude in developing and good resolution.