When the Y chromosome of aMus musculus domesticusmouse strain is placed onto the C57BL/6J (B6) inbred genetic background, the XY (B6.YDOM) progeny develop ovaries or ovotestes, but not normal testes, during fetal life. At puberty, while some of the hermaphroditic males become fertile, none of the XY sex-reversed females produce litters. We have previously demonstrated that the eggs ovulated from the B6.YDOMovary undergo fertilization efficiently, but cannot develop beyond the 2-cell stage eitherin vivoorin vitro.In the present study, we collected oocytes directly from the XY ovary, and examined their maturation, fertilization, and embryonic developmentin vitro.The results show that the juvenile XY ovary yielded far more fertilizable oocytes by direct collection andin vitromaturation than throughin vivoovulation, but the majority of fertilized eggs failed to reach the blastocyst stage. Hence, developmental incompetence of oocytes in the XY ovary appears to be programmed during oocyte differentiation or growth. Nonetheless,in vitromatured oocytes showed a higher potential of embryonic development than the ovulated eggs, suggesting that fertility of the XY female may be impaired by multiple factors. We hypothesized that poor responsiveness of the XY ovary to gonadotropins, as we have previously demonstrated in testosterone production, may impair follicular development or proper recruitment of oocytes for ovulation. In the present study, we compared125I-hCG binding in XX and XY ovaries, but did not find a significant difference. Hence, LH activity appears to be impaired after receptor binding in the XY ovary. On the other hand, the pattern of125I-hCG binding indicated that the majority of antral follicles in the XY ovary failed to undergo normal preovulatory phases, which may explain the lower developmental capacity of eggs after ovulation.