Xenopus laevis oocytes with intact follicle cells were induced to undergo maturation in vitro under the influence of progesterone and related steroids. Injection of the hormone also induced maturation suggesting that the hormone does not need to act on the egg cortex but can interact directly with the cytoplasm. Cytoplasm from in vivo or in vitro maturing or mature oocytes is able to induce maturation when injected back in non-stimulated oocytes. Isolated germinal vesicles do not break down in a medium containing progesterone. Actinomycin D at concentrations as high as 50 μg/ml, did not prevent maturation. However, puromycin and cycloheximide completely suppressed it. These results suggest that protein synthesis is required for maturation while RNA synthesis is not. Since hormone is not itself apparently responsible for the maturational events, some two-step mechanism of hormonal action may be envisioned.