SUMMARYThe replacement time of the human stratum corneum of fifteen body regions was determined by measuring the days required for a strongly substantive fluorescent marker, Dansyl chloride, to disappear. Tbe horny layer was stained by a 24‐h patch exposure to 5% Dansyl chloride (5‐dimethylamino‐ 1‐naphthalene‐sulphonyl chloride) in petrolatum.In most body regions the renewal time for the horny layer was about 2 weeks, in agreement with the findings of other investigators.The advantage of Dansyl chloride over another compound, tetrachlorosalicylanilide, which has been used for this purpose, is that it is not an