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In the rabbit, Kitl mRNA and protein were detected in the squamous granulosa cells of some primordial follicles. The cuboidal granulosa cells surrounding growing follicles uniformly expressed high levels of KITL until the antral stage of development, when the presence of KITL became sporadic. Both mRNA and protein for KIT were detected within all oocytes, at every stage of development. In general, the amount of KIT protein localized to the oolemma increased with follicle growth and then decreased within the fully grown oocytes of antral follicles. The localization of both KITL and KIT protein within the oocytes of some primordial and growing follicles implies receptor activation and endocytosis, as well as receptor replacement. These findings suggest that the KITL/ KIT signaling pathway is active from the earliest stages of follicle development. That only some primordial follicles expressed KITL, whereas KIT protein was expressed within all oocytes, is consistent with a role for KITL and KIT in primordial follicle activation and follicle growth in rabbits.