The B6.Y^TIR mouse fails to develop normal testes despite transcription of Sry, the primary testis-determining gene on the Y chromosome. Consequently, B6.Y^TIR fetuses with bilateral ovaries develop into apparently normal but infertile females. This infertility can be mainly attributed to oocyte incompatibility for postfertilization development. In addition, abnormality in preovulatory follicles and rapid loss of oocytes have been observed in XY ovaries. This study examined the effect of gonadotropins on follicular development and atresia in B6.Y^TIR prepubertal females. The results show that untreated XY females had fewer late preantral follicles and their frequency of atresia was lower. No other difference was found when they were compared with XX females. After treatment with gonadotropins for 24 h, frequency of atresia decreased in both XX and XY ovaries. After 48 h, most preovulatory follicles in XY ovaries were nonatretic, but the oocytes often were denuded. Immunocytochemical staining for connexin 43 detected punctate foci along the oocyte plasma membrane. The density of these foci changed during follicular development, which was similar in XX and XY ovaries. In conclusion, follicular development and atresia under the control of gonadotropins is not influenced by defective oocytes until the preovulatory phase.