AMACR is an essential enzyme in the b-oxidation of branched-chain fatty acids. High expression of AMACR protein is found in prostate adenocarcinoma but not in benign prostate tissue by immunohistochemical staining in paraffin-embedded tissue. The p63 protein, a homologue of the tumor-suppressor p53, is highly expressed in the basal or progenitor layer of many epithelial tissues. P63 is detected in prostate basal cells in normal prostate glands and PIN. However, it is negative in prostate adenocarcinoma. CK 34bE12 recognizes basal cells of benign prostate glands and PIN. Like p63, it is negative in prostate adenocarcinoma. Thus CK 34bE12 and p63 are useful as differential markers for benign prostate glands and adenocarcinoma (negative markers). The combination of AMACR, CK 34bE12 and p63 may be extremely useful for diagnosing PIN and small focus adenocarcinoma, especially in difficult cases and cases with limited tissues.