AbstractFull‐grown stage VIXenopus laevisoocytes (1,200 to 1,300μm) respond to progesterone stimulation by undergoing a series of physiological and morphological changes that are referred to as meiotic maturation. Oocytes in earlier stages of oogenesis (I through V) do not undergo these changes and remain in prophase arrest when exposed to this steroid. We have found that oocytes ranging from 850 μm (stage IV) to 1,000 μm (stage V) are capable of responding to progesterone under the appropriate conditions. Oocytes ≥ 850 μm in diameter underwent germinal vesicle breakdown (GVBD) after 10–12 hr of exposure to progesterone when ouabain was added to the medium at a concentration>2.5 × 10−6M. Under this culture condition, progesterone was now able to induce a 0.3‐ to 0.4‐unit increase in the intracellular pH of stage IV–V oocytes, a 4‐ to 5‐fold increase in 40s ribosomal protein S‐6 phosphorylation, and a 2.3‐fold increase in their rate of protein synthesis. All of these physiological changes are characteristic of full‐grown stage VI oocytes undergoing meiotic maturation. In addition, we have found that oocytes ≥ 750 μm are capable of amplifying maturation promoting factor (MPF) in their cytoplasm leading to GVBD. Therefore, stage IV–VXenopusoocytes have the potential for undergoing meiotic maturation, but they are blocked at a point in prophase that appears to be alleviated by the combin