FSH (follicle stimulating hormone), together with LH (luteinizing hormone), belongs to the gonadotropin family. FSH and LH regulate and stimulate the growth and function of the gonads (ovaries and testes) synergistically.

In women, the gonadotropins act within the hypothalamus‑pituitary‑ovary regulating circuit to control the menstrual cycle. In the ovaries FSH, together with LH, stimulates the growth and maturation of the follicle and hence also the biosynthesis of estrogens in the follicles. The FSH level shows a peak at mid-cycle, although this is less marked than with LH.

Due to changes in ovarian function and reduced estrogen secretion, high FSH concentrations occur during menopause. In men, FSH serves to induce spermatogonium development.

Determination of the FSH concentration is used in the elucidation of dysfunctions within the hypothalamus‑pituitary‑gonads system. The determination of FSH in conjunction with LH is utilized for the following indications: congenital diseases with chromosome aberrations, polycystic ovaries (PCO), amenorrhea (causes), and menopausal syndrome. Depressed gonadotropin levels in men occur in azoospermia.