follicles the follicle culture comprises of at least one culture step which can provide differentiated follicles differentiation is provoked by using suitable media in the method of the present invention media can be divided in three groups a first medium second medium and third medium utilisation of the right medium at the right differentiation stage is crucial for successfully implementing the method of the present invention two examples will illustrate how one can use the method of the present invention with follicles at different differentiation stages when referring to incubation periods the following conditions apply except when otherwise indicated temperature 37 u00b0 c air mixture 5 co 2 in air humidity 100 saturated also the incubation periods may vary to obtain equivalent results when using other species than mouse the examples are optimised for the mouse system an overview of the functions of the specific media as well as an example of their composition can be seen in the following table function first medium second medium third medium differentiation from pre theca to theca cell from secondary follicle to from po follicle to in comprising follicle preovulatory po follicle vitro ovulated metaphase from primary to secondary ii or mature oocyte follicle fixation inhibited fixation to the promoted fixation to the release of a mucified container surface container surface cumulus oocyte complex example u03b1 mem gibco brl 32571 028 u03b1 mem gibco brl 32571 u03b1 mem gibco brl 32571 composition 1 fcs 028 028 its 5 fcs 5 fcs fsh its its lh fsh fsh lh lh hcg egf in the case primary follicles i e follicles with pre theca cells which have not yet differentiated.