Heterogeneity in human androgen receptor (hAR) expression in prostate cancer is considered to be implicated in tumor progression. hAR expression was therefore studied immunohistochemically in localized and locally progressive, hormone refractory (HR) prostate cancer. Because altered functional activity of the hAR may be due to changes in the structural integrity of the hAR gene, exons 2 to 8 of the hAR gene were assessed for mutations by single-strand conformation polymorphism (SSCP) analysis and exon 1 was analyzed for the size of the CAG repeat. The hormone binding capacity, a prerequisite for ligand-regulated receptor function, was determined by a ligand binding assay. Coexpression of the hAR and prostate-specific antigen (PSA) was studied by a sequential double immunoenzymatic staining to verify whether PSA expression is a parameter of hAR function. Almost all human prostatic carcinomas revealed heterogeneous hAR expression, regardless of tumor differentiation and progression. Putative predominance of hAR-negative tumor areas in HR prostate cancer was not observed. No hAR gene mutations or major changes in the CAG repeat were found in the 18 HR carcinomas or in the 9 control samples. Moreover, all selected hAR-expressing cancers were able to bind the synthetic androgen methyltrienolone (R1881). Immunoenzymatic double staining revealed even PSA expression in hAR-negative tumor areas. PSA immunohistochemistry in human prostatic carcinomas therefore is of no use in determining hAR functional activity. Thus, most prostatic carcinomas, even when progressed to a state of hormone insensitivity, contain a structurally intact hAR gene, heterogeneously expressed with retained androgen binding capacity.