The role of LH in ovarian stimulation continues to be controversial. Most observational studies on both gonadotrophin-releasing hormone (GnRH) agonist and GnRH antagonist protocols failed to show an effect on ongoing pregnancy likelihood of punctually measured 'low' or 'high' endogenous LH concentrations during ovarian stimulation. As yet, it is still unknown whether individual patients with strongly suppressed levels of immunoreactive LH would actually benefit from additional LH administration. This can only be explored by means of interventional trials. Most trials on LH supplementation in general populations in both GnRH agonist and GnRH antagonist protocols have not found a benefit of LH supplementation, although it has been indicated that some subgroups, such as older age patients, or patients with a low ovarian response might benefit from LH. These concepts need to be explored further before recommendations can be given as to in who, in what protocol, at what time point and in what doses LH should be supplemented.