Early growth-response (EGR) genes are nuclear transcription factors that are implicated in regulating cell proliferation. Because these genes show divergent expression in various human tumors, we sought to determine their expression in nonmalignant and malignant prostate tissues. Total RNA extracted from prostate tissues was probed with EGR-1, EGR-2, and EGR-alpha cDNA for Northern blots and digoxigenin-labeled cRNA for in situ hybridization. Both Northern blot and in situ hybridization analyses demonstrated increased EGR-1, but not EGR-2 or EGR-alpha expression, in malignant prostate tissue as compared with weak expression in nonmalignant tissue. EGR-1 mRNA was quantified in 96 prostate specimens (86 adenocarcinomas representing different Gleason scores and 10 benign tissues showing no histological manifestation of benign prostatic hypertrophy) using in situ hybridization with an 35S-labeled cRNA probe. EGR-1 mRNA was expressed at significantly higher levels in cancer than in normal prostate (P < 0.001). In cancer with Gleason scores 8-10, the expression of EGR-1 was higher compared with those of lower Gleason scores (P < 0.005). Immunohistochemical staining showed predominately basal cell nuclear EGR-1 protein in prostatic acini. Nuclear staining was weak in nonmalignant tissues, more intense in moderately differentiated carcinoma, and most intense in poorly differentiated carcinoma. These results show that EGR-1 is overexpressed in prostate cancer and suggest a role for EGR-1 in prostate cancer growth.