Positive-working radiation-sensitive mixtures, essentially consisting of(a1) a water-insoluble organic binder which contains acid-labile groups and is rendered soluble in aqueous alkaline solutions by the action of an acid, or(a2.1) a polymeric binder which is insoluble in water but soluble in aqueous alkaline solutions and(a2.2) an organic compound whose solubility in an aqueous alkaline developer is increased by the action of an acid, and(b) an organic compound which produces an acid under the action of actinic radiation, which additionally contain(c) a strongly basic organic compound having hydroxide, alkoxide or phenoxide anions, are suitable for the production of relief structures having improved contrast.