Insulin-like growth factor-I (IGF-I) and IGF-II have been proposed as potential regulators of ovarian function. To gain further insight as to the possible role(s) of the IGFs in human ovarian physiology, we have characterized the expression of the genes encoding the IGFs and their corresponding receptors in the human ovary using solution hybridization/RNase protection assays. IGF-I gene expression was evident in liver, placenta, and whole premenopausal ovary, but not in luteinized granulosa cells. Use of 3'- and 5'-specific antisense RNA probes revealed the presence of IGF-I mRNAs encoding both the Ea and Eb forms of the E-peptide as well as potential 5'-untranslated region splicing variants in liver, placenta, and whole menopausal ovary. Immunohistochemical studies localized the IGF-I peptide to the thecal-interstitial compartment. IGF-II mRNA transcribed from the fetal or fetal-neonatal IGF-II promoter was found in whole premenopausal ovary, luteinized granulosa cells, and placenta. Insulin and type I and type II IGF receptor mRNAs were detected in all tissues examined. Two protected probe fragments were seen with the type I IGF receptor probe in each case, suggesting the possibility of alternate splicing. These studies provide further evidence for a role of these growth factors in human ovarian function.