The mammalian ovarian follicle consists of a multilayered complex of somatic cells that surrounds the oocyte. A signal from the follicle cells keeps the oocyte cell cycle arrested at prophase of meiosis I until luteinizing hormone from the pituitary acts on the follicle cells to release the arrest, causing meiosis to continue. Here we show that meiotic arrest can be released by microinjecting the oocyte within the follicle with an antibody that inhibits the heterotrimeric G-protein Gs. This indicates that Gs activity in the oocyte is required to maintain meiotic arrest within the ovarian follicle, and suggests that the follicle may keep the cell cycle arrested by activating Gs.