Wnt ligands and Frizzled (Fz) G protein-coupled receptors impact cell fate, including embryonic development of the ovary. Because the role of these regulatory molecules during follicular development in the adult is not known, an RT-PCR survey was done. Wnt-4, Fz-4, and Fz-1 were among the transcripts detected, and each exhibited a specific pattern of expression. Fz-1 mRNA was low in preovulatory follicles of PMSG-treated mice but was increased within 4-12 h after an ovulatory surge of human CG. By in situ analysis, Fz-1 transcripts increased first in the theca cells and then in the granulosa cells of ovulating follicles but were low in corpora lutea. In contrast, Wnt-4, a critical factor in early ovarian development, was expressed in small preantral follicles. In addition, Wnt-4 was detected in preovulatory follicles and exhibited high levels in corpora lutea. A potential receptor for Wnt-4 in corpora lutea is Fz-4 that was also elevated in this tissue. Although Wnt-4 has been shown to function downstream of the PR in other tissues, Wnt-4 was not altered in follicles of PR-null mice that fail to ovulate. Rather expression of Fz-1 was lower in ovaries of PR knockout mice, compared with normal littermates. Thus, specific Wnt/Fz are expressed at distinct stages of follicular development, suggesting multiple functions for this signaling pathway in the ovary.