The aim of this thesis was to investigate possible roles for activin, neurotrophin-4 (NT4) and brain derived neurotrophic factor (BDNF), in fetal ovary development. The effects of BDNF on maturation of the bovine oocyte as well as implications for embryo development after parthenogenetic activation were also investigated. Expression of mRNA for the activin βA and βB subunits and activin receptors was demonstrated in the human fetal ovary at 14-21 weeks gestation. Quantitative expression of βA mRNA increased two fold across the gestational range examined. Activin subunits and receptors ALK4, ActRIIA and ActRIIB were localised by immunohistochemistry. The βA subunit was expressed by oogonia, whereas the βB subunit and activin receptors were expressed by both oogonia and somatic cells. βA expression was increased in larger oogonia at later gestations, but was low in oocytes within newly formed primordial follicles. The activin-binding protein follistatin was not detected by immunohistochemistry. Culture of fetal ovary fragments with activin A increased the number of oogonia present as well as oogonial proliferation, as detected by BrdU incorporation, indicating a role for activin in the autocrine/paracrine regulation of germ cell proliferation in the time leading up to primordial follicle formation. Expression and localisation of NT4, BDNF and their common receptors TrkB and p75 was detected in human fetal ovaries, or their supportive somatic cells. The effect of NT4 and BDNF on oogonia survival and proliferation was investigated using an in vitro tissue culture model. Culture of fetal ovary fragments with BDNF, NT4, anti-NT4 or both NT4 and anti-NT4 showed no difference, both in terms of germ cell number and oogonial proliferation, when compared to control groups. However, culture of fetal ovary fragments with BDNF and anti-NT4 showed a significant decrease in number of germ cells, and reduced proliferation, supporting a theory of differential ligand signalling via TrkB / p75 receptors in the human fetal ovary prior to primordial follicle formation. RT-PCR and immunohistochemistry demonstrated that bovine cumulus and oocytes express mRNA and protein for BDNF and the p75 receptor. However mRNA for full length and truncated isoforms of the TrkB receptor were only detected in cumulus, suggesting that oocytes and cumulus differ in their capacity to respond to neurotrophin signalling. In in vitro maturation experiments, the proportion of cumulus oocyte complexes maturing to metaphase II was not altered by BDNF using a serum free maturation system. However, after maturation, the proportion of parthenogenetically activated oocytes forming blastocytes was higher for groups matured with BDNF, an effect that was reversed by maturation in the presence of a BDNF blocking antibody. These results suggest neurotrophins play a role in oocyte maturation by promoting cytoplasmic competence to support early embryonic development.