Renewed interest is being directed toward chemoprevention as a means of reducing cancer mortality. To overcome the inherent problems associated with using cancer development as a study end point, there has recently been a great surge of interest in defining the biomarkers associated with specific stages of the carcinogenic process as intermediate end points. We have detailed the evidence supporting the concept of field cancerization, a concept of general importance that is probably applicable to carcinogenesis and chemoprevention at many organ sites in humans, and presented results of tests of the potentially useful biomarkers proliferating cell nuclear antigen and blood group antigen. Because microassay techniques are more readily applicable to small biopsy samples, further expansion of these studies and exploration of panels of additional biomarkers are expected to generate exciting results in the field of chemoprevention.