The right lower inner arms of 22 healthy test persons in total have been treated either with 6% salicylic acid solution in 70% isopropyl alcohol, or with 5% precipitated sulphur mixture in white petrolatum, or with a surfactant mixture. The basic preparations without active agents have been applied to the corresponding skin area on the left arms. The thickness of the corneal layer on both arms was measured by means of the cantharidin blister method. Salicylic acid, sulphur, as well as the surfactant mixture all led to a more significant reduction of the corneal layer than the basic preparations. Under the chosen test conditions, the keratolytic effect of all three substances has thus been proven.