Insulin-like growth factor (IGF)-binding proteins (IGFBPs) modulate the activity of IGFs. In vitro human prostate epithelial cells secrete IGFBP-2 and -3. In vivo IGFBP-2 is increased, and IGFBP-3 is decreased in the serum of patients with prostate cancer. Immunohistochemistry and in situ hybridization were performed to compare the expression of IGFBP-2 and -3 in vivo in prostate tissue containing benign epithelium, high grade prostate intraepithelial neoplasia (PIN), and adenocarcinoma. Immunoreactivity and messenger ribonucleic acid (mRNA) hybridization signals for IGFBP-2 and -3 were localized to epithelial cells. IGFBP-2 immunostaining intensity was significantly increased in PIN regions compared to that in normal epithelium and was further increased in malignant cells. IGFBP-2 mRNA was also significantly increased in PIN and cancer cells. IGFBP-3 immunoreactivity was significantly increased in PIN regions compared to normal epithelium; however, IGFBP-3 protein was significantly decreased in malignant cells. IGFBP-3 mRNA remained virtually unchanged in benign epithelium, PIN, and adenocarcinoma cells. These results demonstrate that increased IGFBP-2 protein in PIN and malignant cells is probably due to increased mRNA expression. However, levels of IGFBP-3 protein may he due to pre- and/or posttranslational mechanisms, including proteolysis. The changes in IGFBP-2 and -3 protein levels in prostate tissue are in agreement with serum changes reported in patients with prostate cancer.