abstract–The enamel organ from the rat incisor was dissected out. The amount of connective tissue in the samples was checked by light microscopy. Samples representative of the stage of enamel matrix formation and of enamel maturation were taken and the activities of the following enzymes were estimated: aldolase, pyruvate kinase, lactate dehydrogenase, malate dehydrogenase, glucose‐6‐phosphate dehydrogenase and alkaline phosphatase. The enzyme activities were related to the amount of tissue protein and the amount of DNA. All the enzymes, except alkaline phosphatase, showed an increase in measured activity during the stage of enamel maturation. The significance of these changes inin vitroactivities is disc