The ovary has two principal functions: (1) the production of ova, and (2) the secretion of sex hormones. Both functions are intimately interrelated and directed toward successful fertilization, migration of the fertilized ovum to the uterus, implantation of the blastocyst in the endometrium, and early development of the embryo. Disturbances of these functions are clinically reflected in menstrual disorders and infertility. The clinical evaluation of ovarian function is based on the cyclic phenomena elicited by the ovarian hormones on target organs and the direct measurements of these hormones or their metabolites or both in body fluids. This is also true for the diagnosis and detection of ovulation in sterile patients and in women practicing the rhythm method of birth control. In the opinion of some authors the recovery of the ovum in the genital tract or the establishment of pregnancy is the only valid and certain method of diagnosing ovulation.