Luteinizing hormone (LH) is produced in both men and women from the anterior pituitary gland in response to gonadotrophin releasing hormone (GnRH), which is released by the hypothalamus. LH, also called interstitial cell-stimulating hormone (ICSH) in men, is a glycoprotein with a molecular weight of approximately 30,000 Da. In women, LH helps regulate the menstrual cycle and egg production (ovulation). The level of LH in a woman’s body varies with the phase of the menstrual cycle. It increases rapidly just before ovulation occurs, about midway through the cycle (day 14 of a 28-day cycle). This is called an LH surge together during the monthly menstrual cycle. In men, LH stimulates the production of testosterone, which plays a role in sperm production.