Background: rs10993994, a single nucleotide polymorphism (SNP) at the genetic locus encoding â-microseminoprotein (β-MSP), is associated with both prostate cancer risk and levels of blood prostate-specific antigen (PSA), a biomarker used in prostate cancer screening. Therefore, we wished to determine the association between SNPs at MSMB, the gene encoding β-MSP, and the levels of prostate-produced biomarkers β-MSP, PSA, and human kallikrein 2 (hK2) in blood and semen. Methods: Blood and semen from 304 healthy young Swedish men (ages 18-21) were assayed for â-MSP, PSA, and hK2. SNPs around MSMB were genotyped from matched DNA and analyzed for quantitative association with biomarker levels. Empirical P values were multiple test-corrected and the independence of each SNP's effect was determined. Results: rs10993994 was significantly associated with the blood and semen levels of β-MSP (both P < 1.0 × 10-7) and PSA (P = 0.00014 and P = 0.0019), and semen levels of hK2 (P = 0.00027). Additional copies of the prostate cancer risk allele resulted in lower β-MSP but higher PSA levels, and singly explained 23% and 5% of the variation seen in semen β-MSP and PSA, respectively. Additional SNPs at MSMB are associated with β-MSP and PSA independently of rs10993994. Conclusions: SNPs at MSMB correlate with physiologic variation in β-MSP and PSA levels in the blood and semen of healthy young Swedish men. In particular, rs10993994 has a strong effect on β-MSP levels. Impact: Our results suggest a mechanism by which rs10993994 might predispose to prostate cancer and raise the possibility that genetic variation might need to be considered in interpreting the levels of these biomarkers.