We measured several of the components involved in the thiol-disulfide balance of immature and mature oocytes of Xenopus laevis: total soluble native sulfhydryl, reduced and oxidized glutathione, native sulfhydryl content of soluble protein, and disulfide content of soluble protein. None of these values changed during maturation. Both the immature and mature oocyte were characterized by a relatively high disulfide to sulfhydryl ratio. We also measured native sulfhydryl content of germinal vesicle proteins and enucleated oocyte proteins in immature oocytes. Contrary to early cytochemical findings, our measurements suggest that the germinal vesicle has a lower concentration of protein sulfhydryl than does the cytoplasm.