OBJECTIVE This study evaluates the accuracy of comparing serum prostate-specific (PSA) levels in the range between 4.1 ng/mL and 10.0 ng/mL (monoclonal) to the volume of the transition zone (TZ) of the prostate and total gland volume as a predictor of a positive biopsy. METHODS Using sonographic voluming of the entire prostate and of the TZ, prostate-specific antigen density (PSAD) and prostate-specific antigen density of the TZ (PSAT) were calculated in 21 biopsy-positive patients and 38 biopsy-negative patients. Biopsy was directed at sonographically suspicious areas and did not include sextant biopsies. RESULTS A statistically significant association was determined between a positive biopsy and gland volume, TZ volume, and PSAT. The association of a positive biopsy with PSA and PSAD was not statistically significant. CONCLUSIONS PSAT is more accurate in predicting a positive biopsy than is PSAD for PSA levels between 4.1 ng/mL and 10.0 ng/mL.