The canine oocyte offers a very unusual model for meiosis. Its maturation in vitro, studied only for the past 10 years, is still poorly controlled: low rate of metaphase II (10 to 20% vs. >90% in cattle), and high rate of degeneration in cultures (20 to 60%) despite attempts to improve culture media. However, in dogs as well as in other canidae species threatened by extinction, in vitro maturation is a key step for reproductive biotechnologies such as in vitro fertilization and embryo production. It is, therefore, urgent to improve our understanding of the canine oocyte to improve maturation rates. We initiated studies on oocyte maturation in bitches. The role of cAMP in the resumption of meiosis in vitro in bitches using substances which reduce (Rp-cAMP) or increase (dbcAMP and forskolin) its level inside the oocyte was studied. We also used denuded oocytes to prevent any cAMP supply from the granulosa cells. Using this model, we observed that cAMP might play a role in maintaining meiosis, and that the resumption of meiosis may also be controlled by another pathway, possibly involving calcium. Another project explored the changes in the oocyte ultrastructure during in vivo and in vitro maturation. Transmission electron microscopy may provide precise information on possible cytoplasmic anomalies induced by maturation. This fundamental work will eventually help us improve in vitro maturation of canine oocytes.