Interaction of genotoxic chemicals with their intracellular target, i.e., DNA, may result in the formation of covalent adducts. Various methods have been developed to estimate exposure to genotoxic chemicals by means of molecular dosimetry of DNA adducts. Such experiments have generally been carried out with radiolabeled genotoxicants administered in vitro to cultured cells or in vivo to laboratory animals. Biomonitoring of human exposure to genotoxic chemicals requires methods to detect very small quantities of nonradioactive DNA adducts in limited amounts of sample. Attention has been devoted to the development of immunochemical techniques in which specific DNA adducts can be detected with antibodies. The level of sensitivity achieved in these experiments renders these methods applicable for human biomonitoring. When suitable antibodies are available, the immunochemical approach enables one to analyze various types of adducts separately, and to discriminate between irrelevant (e.g., quickly repairable) and relevant lesions (key lesions) with respect to biological end points such as mutation induction and cancer. Polyclonal and monoclonal antibodies were used for the detection of DNA adducts in animal and human tissue. Adducts were measured in DNA from various organs of rats treated with the liver carcinogen 2-AAF. Human exposure to genotoxic agents was studied by the measurement of DNA adducts in blood cells from patients treated with the genotoxic cytostatic cisplatin. Also, the development is described of a system to detect and quantitate DNA adducts at the single-cell level by means of immunofluorescence microscopy, which allows the analysis of small samples of human tissue with preservation of cell morphology.