Free and total prostate specific antigen (F-PSA and T-PSA) in serum were measured with immunoradiometritic assay and the F/T-PSA ratio was calculated in 175 patients with T-PSA levels in the range of 4-20 μg/L. Among them 141 patients were benign prostatic hyperplasia (BPH)

23 were untreated prostate cancer (Pca untreated) and 11 were treated prostate cancer (Pca treated). The results showed that difference in F-PSA and F/T-PSA ratio for BPH group and Pca untreated group were statistically significant (P<0.01). The effectiveness of F/T-PSA ratio for Pca (89.9%) was higher than F-PSA (54.8%). The receiver-operating characteristic (ROC) curve showed an improved diagnostic efficacy of F/T-PSA ratio compared with T-PSA for discrimination between BPH and Pca. If mean F/T-PSA ratio value+ 1SE (13.2%) was used in BPH group as discrimination limits of Pca patients

the diagnostic accuracy of BPH group and Pca untreated group were 90.8% and 82.6% respectively. Thereby F/T-PSA ratio may be useful for the differentiation between BPH and prostate cancer.