The androgen receptor (AR) regulates gene transcription by binding to androgen response elements in target gene promoters. The prostate-specific antigen (PSA) gene has a polymorphic androgen response element sequence with two alleles, A and G. We hypothesize that allelic differences in AR-driven PSA expression may influence prostate cancer risk. To test this hypothesis, we assayed PSA genotype for 57 prostate cancer cases and 156 controls from our previous pilot study in which prostate cancer risk was associated with the AR "CAG-short" genotype. Odds ratios (ORs) were estimated relating prostate cancer risk to AR and PSA genotypes, singly and in combination. Subjects with the PSA GG genotype were at significantly increased risk for advanced, but not for localized, prostate cancer (OR, 2.90; 95% confidence interval, 1.24-6.78). When cross-classifying subjects by AR and PSA genotypes, subjects with either a CAG-short allele (and not PSA GG) or with the PSA GG genotype (and not CAG-short) had a modest, statistically insignificant increase in prostate cancer risk overall. However, subjects with both a short CAG allele and PSA genotype GG had a more than 5-fold increase in prostate cancer risk (OR, 5.08; 95% confidence interval, 1.59-16.25). All of the ORs were substantially greater for advanced prostate cancer. Studies with larger numbers of advanced cases will be needed to confirm these results. These results indicate that polymorphism in the PSA gene promoter influences prostate cancer risk, and that the allelic variation in promoter activity may be androgen-dependent. Furthermore, these results support a multigenic etiology for prostate cancer.