We examined the usefulness of prostate specific antigen alph-1-antichymotrypsin complex (PSA-ACT) and its indices for the detection of prostate cancer in patients with a prostate specific antigen (PSA) level between 2.1 and 10.0 ng/ml. Between July 1999 and October 2001, 151 patients with a PSA level between 2.1 and 10.0 ng/ml underwent a systematic biopsy under transrectal ultrasound (TRUS) guidance. The clinical values of total PSA, PSA-ACT, PSA density (PSAD), PSA-ACT density (PSA-ACTD), PSA transition zone density (PSATZD) and PSA-ACT transition zone density (PSA-ACTTZD) for the detection of prostate cancer were compared by using receiver operating characteristic (ROC) curve analysis. Of the 151 patients, 36 (23.8%) were histologically confirmed as having prostate cancer. The differences between patients with prostate cancer and benign prostatic disease were significant with respect to the PSA and PSA-ACT related parameters examined in this study. According to ROC curve analysis, the area under the curve (AUC) of PSA-ACTTZD was the greatest of all the parameters. The differences was significant between the AUC of PSA-ACTTZD and total PSA (p < 0.05). The cutoff value of PSA-ACTTZD with 0.20 ng/ml2 showed the highest sum of sensivitity (90%) and specificity (55%). Also, in 86 patients with a PSA level between 2.1 and 6.0 ng/ml, the AUC of PSA-ACTTZD was the greatest of all the parameters. Measuring the level of PSA-ACT and its indices may provide a better differentiation of prostate cancer and benign prostatic disease than total PSA alone in patients with intermediate PSA levels. PSA-ACTTZD is the most useful indicator among PSA-ACT and its volume indices.