This study describes a model for short-term culture of intact mouse follicles under serum-free conditions. Follicles were either obtained from immature mice receiving no ovarian stimulation (i.e. no eCG-primed protocol, group I) or from mice undergoing ovarian stimulation (i.e. eCG-primed protocol, group II). Follicles were grouped according to size (100–170, 180–200, 210–250, 260–350 and 360–400μm, respectively) and cultured for 24h (group I) or for only 6h (group II). Induced meiotic resumption of follicle-enclosed oocytes were evaluated following stimulation with gonadotropins (i.e. FSH and hCG), AY9944-A-7, an inhibitor of Δ14-reductase, and RS-21745, an inhibitor of lanosterol 14α-demethylase; both enzymes affect synthesis of the meiosis activating sterols (MAS) that induce oocyte maturation. The frequency of oocyte degeneration was also recorded. In group I, FSH (10–200IUl⁻¹) and AY9944-A-7 (5, 25 and 50μM) separately induced resumption of meiosis in oocytes derived from follicles with a diameter of 180–400μm. hCG (1.0 and 10IUml⁻¹) exhibited a similar but weaker effect on oocytes present in follicles with a diameter of 260–400μm. Irrespective of follicular diameter oocytes obtained from follicles in group II responded to hCG and FSH by resuming meiosis. FSH (50IUl⁻¹) alone or hCG (10IUml⁻¹) alone both increased the GVBD percentage of oocytes enclosed in follicles with a diameter 260–400μm, but the response to hCG was not significant compared to control. FSH (50IUl⁻¹) combination with hCG (10IUml⁻¹) showed an additive effect raising the rate of GVBD after 6h culture. Addition of 50 or 100μM RS-21745 was able to attenuate gonadotropins-induced resumption of meiosis to below background levels. In conclusion, the ability of FSH to induce meiotic resumption of follicle-enclosed mouse oocytes is correlated to follicle size, being most pronounced in larger follicles. hCG caused a similar but less pronounced effect. The ability of RS-21745 to inhibit and the ability of AY9944-A-7 to enhance oocyte maturation of follicle-enclosed oocytes support the concept of FSH employing MAS as a downstream signal transduction molecule for initiation of oocyte maturation in mice.