Histoenzymorphologic investigations on β-D-glucuronidase in cortical granules in oocytes of some representative vertebrates revealed interesting differences in localisation of the enzyme in the two techniques employed using 8-hydroxyquinoline β-D-glucosiduronic acid and naphthol AS-BI β-D-glucosiduronic acid as substrates. In the former a nonspecific localisation in the entire cytoplasm of the oocytes excepting nucleus was evident whereas in the latter the cortical granules alone exhibited intense activity. To some extent this difference could be accounted for on the basis of yolk content of the eggs. β-D-glucoronidase-rich lysosomal cortical granules were found in the amphibian, reptilian and avian oocytes whereas mammalian oocyte cortical granules were devoid of this enzyme. β-D-glucuronidase in cortical granules was sensitive to low concentrations of Hg++, Cu++, glucuronic and mucic acids. Other histochemical evidence for the lysosomal nature of the cortical granules is presented and discussed. β-D-glucuronidase seems to have a role in ovum-nutrition and activation which, thus, make a new addition to the existing knowledge of physiological role of β-D-glucuronidase and lysosomes.