Knowledge of the physiology of folliculogenesis has led to a better understanding of the role of LH activity in this process. This role has been investigated in the setting of ovarian stimulation and several treatment modalities have been proposed. LH activity can be provided in the forms of: (i) human menopausal gonadotrophins (HMG), (ii) recombinant LH (rLH), (iii) human chorionic gonadotrophin (HCG), and (iv) recombinant HCG (rHCG). Current evidence suggests that ovarian stimulation performed with HMG in patients treated with a long gonadotrophin releasing hormone (GnRH) agonist protocol seems to result in increased (3-4%) clinical pregnancy rates compared with recombinant FSH (rFSH). Data regarding the short GnRH agonist or GnRH antagonist protocol are scarce and firm conclusions cannot be drawn. Administration of rLH prior or during ovarian stimulation with rFSH does not seem to increase the probability of pregnancy. Existing data suggest that HCG is capable of partially or completely replacing FSH administration during the mid-to-late follicular phase of an ovarian stimulation cycle, leading to a decreased requirement for FSH, without compromising pregnancy rates. High quality evidence originating from randomized controlled trials regarding the potential value of rHCG administration during ovarian stimulation for IVF is not available.