PIP: The changing flow of ovarian signals apparently regulates the nature of the activities of the hypothalamic-pituitary unit. The ovary has many putative intraovarian regulators. It has many compartments, each with a different and variable biological property. The ovary's follicular compartments respond to cyclic pituitary gonadotropin secretion by secreting sex steroids and producing a fertilizable ovum. Operational characteristics of the ovary include steroidogenesis and biosynthesis of estrogen, progestin, androgens, and proteins. The proteins are inhibin, activin, follistan, and gonadotropin surge inhibiting factor. Signalling systems comprise an established ovarian regulator. Follicle stimulating hormone promotes follicular maturation. Luteinizing hormone contributes greatly to maintaining the corpus luteum function and may also have a follicular role. Estrogens have multiple roles: they promote cellular division and intercellular gap junction formation and act synergistically with gonadotropins at various levels including promotion of ovarian growth. Androgens also have several roles (e.g., a variety of receptor-mediated effects at the level of the granulosa cell). Ovarian cyclicity consists of follicular growth and development, ovulation, and corpus luteum formation and demise. Follicular growth and development has three stages, all of which are regulated by steroid hormones: recruitment (follicle leaves the resting pool to begin growth and development), selection (final separation of the maturing follicular cohort down to a size equal to the species-characteristic ovulatory quota), and dominance (status of the follicle destined to ovulate). Ovulation is rapid follicular enlargement followed by protrusion of the follicle from the surface of the ovarian cortex. Following ovulation, the dominant follicle reorganizes and becomes the corpus luteum. Estrogens and prostaglandins may contribute to the destruction of the corpus luteum. Operational characteristics of the ovary are crucial to finding a new and improved contraceptive technology.