AIMS: Uridine diphosphate-glucuronosyltransferase 2B (UGT2B) enzymes conjugate testosterone metabolites to enable their excretion in humans. The functional significance of the UGT2B genetic variants has never been described in humans. We evaluated UGT2B variants in relation to plasma androstane-3α,17β-diol-glucuronide (AAG) levels and the prostate cancer risk. RESULTS: AAG levels were measured in sera from 150 controls and compared to the polymorphisms of UGT2B17, UGT2B15, and UGT2B7. Genomic DNA from controls (301) and cases (148) was genotyped for the polymorphisms, and odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated using unconditional logistic regression analyses. Having two copies of UGT2B17 was associated with higher AAG levels in controls among Whites (p=0.02), but not Blacks (p=0.82). Logistic regression models adjusting for age and race revealed that homozygosity for the G allele of the UGT2B15(D85Y) polymorphism was directly associated with the prostate cancer risk (OR=2.70, 95% CI=1.28, 5.55). CONCLUSIONS: While the small sample size limits inference, our findings suggest that an association between the UGT2B17 copy number variant (CNV) and serum AAG levels in Whites, but unexpectedly not in Blacks. This novel observation suggests that genetic determinants of AAG levels in Blacks are unrelated to the UGT2B17 CNV. This study replicates the results that show an association of UGT215(D85Y) with an increased prostate cancer risk.