PSA is the most important of all tumor markers because it has significant applications in all aspects of the management of men with prostatic disease. Certainly, the most important utilization of PSA is for early detection of this most ubiquitous of all human neoplasms. In this article the authors describe the molecular forms of PSA and their characteristics, the factors influencing values of serum concentration of PSA, the problems of screening, and particularly the possibility to use PSA for detection of prostate carcinoma. A big problem in prostate carcinoma detection is the low specificity of PSA at the concentrations between 4-10 ng/ml, the so-called diagnostic gray zone, where the incidence of prostate carcinoma is only 25%. The authors evaluate the methods which make it possible to increase the sensitivity and/or specificity of PSA detection, such as PSA density, PSA density of the transition zone, PSA velocity, PSA doubling time, age-specific PSA, free PSA and, prospectively, the use of the RT-PCR technique.