Samples of epidermis about 50 mg. in wt. and 0.12-0.18 mm. in thickness were cut from the skin of normal persons and of persons suffering from the skin disease vitiligo and placed in 30 ml. Ringer soln. for 90 min. under N2. Respiration measurements were made in the Warburg apparatus at 37[degree]. Qo2 for the skin of normal subjects was [long dash]1.29, while Qo2 for depigmented, normally pigmented and over-pigmentcd skin of patients suffering from vitiligo, was, respectively,[long dash]0.67,[long dash]0.67, and[long dash]0.68. The addition of the substrates glucose, dioxyphenylalanine and cadaverine did not increase the respiration of the vitiligo skin to normal. Addition of the catalytically active substances adermine, nicotinic acid amide, aneurine and pantothenic acid also had no effect. The skin of normal persons was burned slightly with CO2 snow and the contents of the blisters removed after 48 hrs. When this untreated, heated or dialyzed material was added to the respiration mixtures, Qo2 for the vitiligo skin increased from [long dash]1.78 to [long dash]2.5. The active factor in the blister contents was'' of low mol. wt. and was thermostable.