The follicular growth takes longer in most mammals than it does in rodents: (4 to 15 days between the antral stage and ovulation in rodents, versus 65 days in women). The ovulation rates typical of animal species are mainly regulated during two critical periods: antrum formation and a few days before ovulation. The FSH level appears to be determinant, but in the animal species or races whose ovulation rate is near one, a dominant follicle is involved in the atresia of others. Increasing the level of gonadotrophins, especially of FSH, results in superovulation. However, the results are often irregular, with prolonged maturations and ovulations and oocytes of uncertain quality. Using pituitary gonadotrophins instead of placental or urinary hormones considerably increases the number of oocytes available and improves the development of embryos if the FSH/LH ratio of pituitary gonadotrophins is adjusted to the species involved. Thus, the main problem concerns the quality of the oocyte. At the present time, no criterion allows a prediction of the quality of the oocyte, and the complexity of the mechanisms involved in its intrafollicular maturation do not foreshadow a simple and rapid solution. However, appreciable improvements in our techniques are possible on the basis of current knowledge.