According to the two-cell-two-gonadotrophin theory and the LH therapeutic window concept the role of endogenous LH in folliculogenesis and ovarian steroidogenesis is broadly accepted. Current discussions are aimed at necessity and benefit of exogenous LH administration during ovarian stimulation in IVF cycles. The number of opinions on the necessity of exogenous LH applications in certain groups of patients for achieving good stimulation response is increasing. Currently more types of commercial gonadotrophin preparations with different composition and various pharmacodynamics are available. Better knowledge of mechanism and dynamics of LH effect in folliculogenesis convey rational selective application of gonadotrophins with LH activity and thus enhances security and successfulness of treatment. Following discussion on threshold and ceiling LH levels has been proceeding to this day and in the future will definitely bring further new knowledge. All types of gonadotrophins and their combinations have their own role in ovarian stimulation. The choice of gonadothropins with LH activity, its dosage and the onset of administration should be balanced.