Assays for detecting and determining the presence of prostate cancer is provided. The assays are capable of detecting prostate cancer in the population of men with a significantly higher ratio of free PSA to total PSA. The assays are also capable of detecting prostate cancer in the population of men with a low amount of total PSA, i.e., in the range of 2 to 4 ng/ml. In accordance with one embodiment of the present invention, the assay includes the steps of (a) determining the amount of total PSA contained in a biological sample from the patient, (b) determining the amount of free PSA in the sample; and calculating the ratio of the free PSA to the total PSA, (c) determining the amount of pPSA in the sample, (d) determining the amount of BPSA in the sample, (e) determining the amount of inPSA in the sample, and (f) correlating the amount of inPSA contained in the sample to the presence of prostate cancer in the patient by comparing the amount of inPSA to a predetermined value established with control samples of known cancer and benign disease diagnosis, based on both the level of total PSA and the % free PSA.