Intraovarian growth factors play a significant role in the regulation of follicular selection and growth. In this study, the presence and localization of all members of the family of platelet-derived growth factors (PDGF) and receptors (PDGFR) were identified and characterized in the rat ovary. In addition, a role was identified for members of this family in contributing towards growth of preantral follicles. Real-time PCR revealed the presence of mRNA for all platelet-derived growth factors (Pdgfa, Pdgfb, Pdgfc and Pdgfd) and receptors (Pdgfra and Pdgfrb) in the rat ovary from birth until 4 wk. In situ hybridization and immunohistochemistry were utilized to identify cell-type expression of PDGFs and PDGFRs in rat ovaries from birth until 4 wk. Shortly after birth, expression of PDGFRA and PDGFC was observed in and around oocyte clusters, and PDGFRB in stromal cells surrounding oocyte clusters. All members were identified in oocytes of primordial and primary follicles, and in cells of the theca layer of primordial to antral follicles. PDGFRA and PDGFA were also localized to some granulosa cells of secondary and antral follicles in ovaries from rats at Days 20 and 24. Thus, localization data suggest both theca-theca and theca-granulosa cell interactions of PDGFs and receptors. Preantral follicles cultured in vitro over 5 days in serum-free medium plus recombinant PDGFAA, PDGFAB, or PDGFBB increased in follicle diameter by 18.32% ± 2.18%, 17.72% ± 2.3%, and 17.6% ± 1.81%, respectively, representing significantly greater increases than for follicles incubated in serum-free medium alone (11% ± 1.57%), and suggesting a role for these growth factors in positively influencing early follicle growth.