In this chapter, the authors focus on the first successful artificial neural network (ANN) for distinguishing men with palpable cancers from healthy volunteers with prostates that felt normal. They distinguish volunteer men with normal-feeling benign prostatic hyperplasia regardless of the level of their serum prostate specific antigen prostate-specific antigen (PSA). Total creatine kinase (CK) seems to play an important role in detecting prostate cancer with a low serum PSA and, interestingly, the lower the total CK the greater the probability of prostate cancer in the ANN. Cancer detection rates in the 90% of all men 40 to 80 years old who have a PSA < 4.0 ng/mL are a fraction of those in the 10% of all men who have a PSA > 4.0 ng/Ml. The ratio of free/total serum PSA was determined at the Department of Urology at Stanford using the Tosoh assay for total serum PSA and the Diagnostic Products Corporation assay for free PSA.