The enzymeβ-glucuronidase (E.C. 3.2.1.31.) has been studied in developing teeth and bone of Sprague-Dawley rats and Macaque monkeys(Macaca Irus)by means of histochemistry using naphthol-AS-B1-β-D-glucuronide as substrate and hexazotized pararosanilin as coupling reagent. Sinceβ-glucuronidase is sensitive to fixatives a freeze-sectioning technique has been used which made it possible to section highly mineralizcd tissues without previous fixation and decalcification. In the bone enzyme activity was found in osteoclasts and osteoblasts.β-glucuronidase activity was found in teeth of both species in odontoblasts, ameloblasts, stratum intermedium, inner and outer enamel epithelium. When enamel matrix formation was completed as indicated by the reduction of ameloblast length the enzyme activity of the ameloblasts increased.