As more is learned about the biomolecular properties and physiology of the glycoprotein, prostate-specific antigen, its clinical usefulness with regard to the diagnosis and management of prostate cancer also will improve. Recent advances, including the development of the concepts of prostate-specific antigen density and velocity as well as the discovery that prostate-specific antigen exists in the serum in several molecular forms, will further improve the clinical utility of this tumor marker. The even more recent discovery that the serum prostate-specific antigen is dependent upon age also has the potential to enhance the clinical usefulness of this tumor marker with regard to the early detection of prostate cancer.