The normal distribution of values was determined and the age-related reference ranges were established for free PSA, total PSA and free PSA/total PSA ratios. A total of 414 healthy males (14 to 84 years old) were randomly chosen from the Chinese residing in the central area of Taiwan and underwent detailed clinical examinations that included digital rectal examination and serum PSA determination to exclude the presence of prostate cancer. Free PSA, total PSA, and free PSA/total PSA ratios were determined for each participant. Free PSA and total PSA and free PSA/total PSA ratios correlated directly with case age. However, with regard to free PSA/total PSA ratios, these ratios were constant and none correlated with case age. Using the 95th percentile as the upper limits of normal, the recommended age-related reference ranges for free PSA, total PSA and free PSA/total PSA ratios respectively, are 0.63, 1.50, ng/ml and 64% for healthy Chinese men < 40 years old; 0.55, 1.88 ng/ml and 68% for men 40 to 49 years old; 0.63, 2.37 ng/ml and 68% for men 50 to 59 years old, and 1.32, 4.82 ng/ml and 59% for men 60 to 69 years old; and 1.65, 5.86 ng/ml and 51% for men > or = 70 years old. In comparison with the previous reports from other ethnic populations, a relationship with ages was also found and the appropriate upper limits of normal for free PSA, total PSA and free PSA/total PSA ratios were similar in Chinese males.