The presence of 5-nucleo-tidase, ATPase, and purine nucleosidase activity was demonstrated in the uterine and cervical fluids which accumulate in response to mating or stimulation with certain hormones, as well as in the endometrial secretion produced in the progestational phase of rabbit pregnancy. The endometrial and cervical mucosae also contained these enzymes. Rabbit serum, peritoneal fluid, and seminal plasma contained purine nucleosidase; the seminal plasma in addition contained 5-nucleotidase and ATPase. Unimplanted 6-day old rabbit blastocysts were devoid of 5-nucleotidase and nucleosidase activity but were capable of de-phosphorylating ATP. Blastocyst fluid at 7- 8 days of pregnancy contained no nucleotidase or ATPase but showed some purine nucleosidase activity.