Expression of the messenger ribonucleic acids (mRNAs) for insulin-like growth factors (IGFs), their binding proteins (IGFBP1 through IGFBP-6), and receptors was examined in normal and polycystic human ovaries (PCO). Northern and dot blots and RT-PCR were used to evaluate mRNA levels. The IGF system was studied in fresh granulosa, stromal, and thecal samples and in thecal tissue after incubation with LH and GH. IGF-II expression was high in granulosa and thecal compartments, whereas IGF-I was only weakly detectable, suggesting the importance of IGF-II in the human ovarian IGF system. Northern blot analysis revealed IGFBP-2 and -4 mRNA in all ovarian compartments and IGFBP-5 mRNA in stroma and theca. IGFBP-2 mRNA was the most abundant IGFBP mRNA in the human ovary. No IGFBP-1 or -3 mRNA was detected in fresh ovarian tissues. IGFBP-6 and type 1 and 2 IGF receptor mRNA expression was detectable in all ovarian compartments only by RT-PCR. In cultured theca, the expression of IG-FBP-1, -3, and 4 was induced. Only IGFBP-5 expression showed some dependence on trophic hormone (LH) stimulation during theca incubation. Otherwise, GH and LH had no effect on IGF or IGFBP expression in thecal tissue. This study indicates that thecal tissue is an essential part of the IGF system in the human ovary. However, no differences were found between normal ovaries and PCO in IGF, IGFBP, or IGF receptor expression. Thus, our results (from a limited number of patients) together with recent in situ hybridization and immunohistochemistry data of others provide no evidence for a role for IGFs in the functional disturbances related to PCO. Interestingly, our data show that in cultured thecal samples, the IGF and IGFBP expression pattern is different from that in fresh tissue.