Abstract: The composition consists of an aqueous solution of nitric acid and nitrous acid with a pH below 1 and an acid equivalent of from 6 to 10 mmole/ml; the amount of nitrous acid corresponds to 0.01 to 5 mg of nitrite (NO.sub.2.sup.-) per ml. Additionally, the solution preferably contains acetic acid, oxalic acid and lactic acid as well as copper and cadmium ions. For the preferred composition, the preparation takes place by mixing the components and letting them react to the end or by an oxidative method, in the course of which nitrous acid is formed. The composition is suitable for the local treatment of superficial lesions of the skin and mucous membranes in the fields of cosmetics and medicine, particularly for certain malignant tumors. Experimentally, the effectiveness can be checked by two biological tests developed for this purpose.