The in-vitro growth of immature oocytes in early follicles from cryopreserved human ovarian tissues is a new concept in in-vitro fertilization programmes for the treatment of infertile and cancer patients. To better understand the regulatory mechanism of follicular development, immunohistochemistry was used to study the expression of insulin-like growth factor (IGF) type I receptor (IGF-IR) and transforming growth factor-beta (TGFbeta) type I (TbetaR-I) and type II (TbetaR-II) receptors in fresh and frozen ovarian tissues from 14 women. Immunoreactivities for IGF-IR and TbetaR-I were present simultaneously in the oocytes of primordial, pre-antral and antral follicles. Staining for both IGF-IR and TbetaR-I was also observed in granulosa cells of primordial, pre-antral and antral follicles. IGF-IR and TbetaR-I also stained in thecal cells of pre-antral and antral follicles. Stromal cells in surrounding ovarian tissue expressed IGF-IR and TbetaR-I at various follicular stages. Unlike TbetaR-I, TbetaR-II was expressed only in the oocytes of primordial and primary follicles, and with weak staining intensity in thecal cells. No significant staining for TbetaR-II was found in oocytes and granulosa cells of antral follicles. There was no difference in staining patterns for IGF-IR, TbetaR-I and TbetaR-II between fresh and frozen ovarian tissues, indicating that cryopreservation might not significantly alter the immunoreactivities of these receptors in frozen ovarian tissue. The results suggest that IGF-I and TGFbeta may participate in the regulation of follicular growth by binding to their receptors through an autocrine or paracrine mechanism. IGF-I and TGFbeta may be useful in regulating the in-vitro or in-vivo maturation of oocytes not only in later follicles but also very early follicles, from cryopreserved ovarian tissues for clinical use in the future.