Cutaneous methods for measurement of substrates in mammalian subjects are disclosed. A condition of the skin is used to measure a number of important substances which diffuse through the skin or are present underneath the skin in the blood or tissue. According to the technique, an enzyme whose activity is specific for a particular substance or substrate is placed on, in or under the skin for reaction. The condition of the skin is then detected by suitable means as a measure of the amount of the substrate in the body. For instance, the enzymatic reaction or by-product of the reaction is detected directly through the skin as a measure of the amount of substrate. Polarographic electrodes or enzyme electrodes are employed as skin-contact analyzers in the transcutaneous measurement of oxygen or hydrogen peroxide to quantitatively determine blood substances such as glucose and alcohol. In a preferred quantitative technique, the skin is arterialized, i.e., heated or otherwise treated to arterialize the skin capillaries when the measurements are made. Colorimetric detection methods are also employed.