This chapter deals with different gonadotropin molecules in ovarian stimulation. Human menopausal gonadotropins consist of a purified preparation of gonadotropins extracted from the urine of postmenopausal women. In the natural cycle both follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are required for normal follicular growth and maturation. The main risk associated with the use of FSH-containing gonadotropin products is the development of ovarian hyperstimulation syndrome (OHSS). OHSS can be easily prevented by starting with a relatively low dose of gonadotropin, especially in high-risk women like young patients, those with polycystic ovary syndrome (PCOS), and those with a low body mass index (BMI). From the many randomized trials that have been performed it appears that all available gonadotropins are comparably effective and safe. The differences in isoform profile did not appear to have significant clinically significant effects in in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) cycles.