1. The β-glucuronidase activity of suspensions of mixed white cells, obtained from human blood by the centrifuging technic or by flotation on gum acacia, has been studied.
2. The correlation between β-glucuronidase activity and total white-cell count was greater than that between the activity of the enzyme and either the polymorphonuclear leukocyte count or the lymphocyte count.
3. On the average, the ratio of the enzyme activity in the polymorphonuclear leukocyte to that of the lymphocyte was 5:4.