Alkaline phosphatase level was measured in parts of the reproductive system of laying White Leghorn females of a random bred control line and it was markedly higher in the ovary than in the oviduct, egg yolk, egg white and vitelline membrane. Within the ovary the highest levels were observed in the membranes of large follicles, whereas levels were very low in contents of these follicles. A line with a high level of phosphatase in blood serum did not differ from the random bred control line in the phosphatase level of ovarian follicle membrane or vitelline membrane. However, it had a significantly higher level of the enzyme in egg yolk and ovarian follicle contents, as well as in blood serum. The role of alkaline phosphatase in the functioning of the ovary is discussed.