I. Introduction Alkaline phosphatase is an enzyme widely distributed in various tissues of the body. There are only few reports concerning alkaline phosphatase* in skin disease, and the norms for healthy tissue have not been completely established. It was the purpose of this work to perform adequately controlled investigations in order to elucidate the distribution of AP in normal human skin and in 68 dermatologic conditions. A. The Physiologic Significance of Alkaline Phosphatase Although AP is found in all organs of the body, its role in the physiology of organs, other than bone, is more or less obscure. The physiologic role of AP is best understood in the processes of calcification and ossification.47,50,59,83,88,100,101,119,140 Alkaline phosphatase is also found histochemically in certain sites of fibroplasia,6,11,16,30,36,55,70,78, 121,142,166,182 inflammatory reaction,83,162, glandular secretion,31,37,39,40,48,49,122,147,165, 166 absorption and resorption by epithelium, histodifferentiation,92,93,135,137 and transmembranous solute passage,138 but