Preliminary information of the general enzymatic characteristics of the normal stages of the development of endochondral bone in the dog and the effect of age are presented. The enzymes glucose-6-phosphate, lactic and malic dehydrogenase, and phosphoglucoisomerase are found to be active through the maturing stages of epiphyseal development. Alkaline-phosphatase activity, on the basis of acid-insoluble material comprising the area, is greater in the primary spongiosa than in other locations, as reported previously. The results are discussed in relation both to the total and the acid-soluble solid and phosphorus content in the areas. An over-all increase in the level of enzyme activity is noted in the epiphyseal plate as the newborn dog matures. The enzyme content in the epiphyseal plate is such as to indicate that the process of epiphyseal growth and bone formation is an enzymatically regulated sequence deriving energy and intermediates through the Embden-Meyerhoff pathway, the hexosemonophosphate shunt, and the tricarboxylic-acid cycle. Adaptations of microchemical techniques suitable for chemical investigation of biopsy material from diseased epiphyseal plates are presented.