In assisted reproductive medicine the controlled ovarian hyperstimulation enables several oocytes to be collected with the following transfer of more than one embryo and a higher pregnancy rate than in natural cycles. The most frequently used stimulation protocols are: i) clomiphene citrate (CC) and hMG stimulation; ii) hMG/FSH stimulation; iii) GnRH agonist (GnRH-a) and hMG/FSH stimulation, iiia) GnRH-a long protocol, iiib) GnRH-a short protocol, GnRH-a ultrashort protocol, iv) GnRH antagonist and hMG stimulation. The protocols are described and the advantages and disadvantages are discussed.