Background: In any branch of toxicology it is important to be able to measure the exposure to a toxic agent, the extent of any toxic response, and also to predict the likely response. Tools that enable this to be done are called biomarkers. Therefore, in order to assess the health risks of exposure to potentially toxic chemicals, biomarkers are essential. Biomarker may be divided into: biomarker of exposure, biomarker of response or toxic effect and biomarker of effect. Aim of the work: Introduce and establish the basic knowledge about biomarkers in toxicology for further researches, focusing on new biomarkers in toxicology and DNA adduct, biomarkers have role in in early diagnosis of organ toxicity and finally to know new application of biomarkers in toxicology.