In the periosteum of newborn, 8-, 30- and 60-day-old albino rats, β-glucuronidase, β-galactosidase and succinate dehydrogenase were found. The enzymes of the investigated age groups show remarkable differences in reaction. β-Glucuronidase reacts distinctly in the cells of the cambium layer of 8- and 30-day-old animals. β-Galactosidase reacts very differently in the cell layers of the periosteum of albino rats in all age groups. The reaction of succinate dehydrogenase we found above all in the cambium cells, the preosteoblasts and the osteobla