Occupational health is a priority issue for governments and industries. Monitoring work environment and worker’s health has been traditionally assessed clinically and, at present, by chemical and biochemical assays. These tests may include detection of a specific enzyme activity, concentration analysis of the “parent” compound or its metabolic products in blood, urine or hair among other biological samples. Occupational toxicology is the study of hazardous substances in the occupational environment and the mechanisms of action of these compounds in workers. Chronic chemical exposure is related to the development of diseases that reduce the quality and expectancy of life. On the other hand, industry will benefit from workers health since better sanitary conditions lead to higher production efficiency. Several toxicants such as lead, mercury, cadmium, hydrocarbons, and volatile compounds among others are sources of chronic damage to cells, tissues and organs of exposed workers. For example, it is well known that continuous exposure to asbestos may lead mesothelioma with several health and economic consequences to the worker and the industry. Other example is the chronic exposure to pesticide in agroindustry and the resulting reduction of life expectancy, as well as neuronal and reproductive damage. On other hand, the analysis of potential accumulative damage of exposure to toxicants and individual susceptibility cannot be established by traditional methods. Therefore, the aim of this presentation is to discuss the potential of molecular biology techniques as key tools for the evaluation of the chemical toxicants damage to workers health. Molecular biology and its techniques can contribute to increase feasibility and accuracy of diagnostics. At present Occupational Toxicology has incorporated these novel methods to evaluate risks and assess damage at different levels. These tools include analysis in vitro, evaluation of gene expression, the use of “omic” sciences and bioinformatics. In vitro assays include toxicological tests in cell cultures which may resemble the potential damage on individuals; moreover, these techniques may help to identify molecules such as proteins that alter its structure as a consequence of the contaminants exposure leading to loss of their normal physiological function. Determining changes in gene expression by toxicants is another useful way to evaluate damage. For instance, one of our studies demonstrated that exposure to polycyclic aromatic hydrocarbons (PAHs) in an in vitro model activated and repressed several gene families related to proliferation, DNA repair and adhesion among others. This report showed the potential use of gene expression as a biomarker of exposure. Biomarkers or biological indicators are either measurable changes at the physiological, biochemical or morphological level or specific genetic features in the potentially affected organisms by toxicants exposure. A biomarker is useful to detect exposure, determine the biological consequences of such exposure, and to evaluate initial or intermediate stages of pathological processes. Therefore, identification of molecules that help to distinguish if an abnormal process is developing may become critical to health. Such is the case of CYP2E1 where gene expression increases in blood peripheral lymphocytes obtained from shoemakers and was associated to solvent exposure. As a result CYP2E1 may be considered as biomarker of exposure. Further studies may help to translate these results into clinical diagnosis kits. “Omic” sciences such as genomics, transcriptomics, proteomics and metabolomics may help to integrate data and determine susceptibility among workers. These techniques include analysis of genomes, whole expression analysis at mRNA or protein levels and quantification of metabolites at different conditions. Data obtained with “omic” methods reveal how a toxicant exposure may alter normal parameters or how individuals may be more susceptible due to specific genetic characteristics. Another example is the use of polymorphisms analysis of genes related to xenobiotic metabolism to determine susceptibility to a certain toxicant in individuals. For instance, in several PAHs occupationally-exposed populations around the world genetic variants of CYP450 have been associated with increased risk of cancer development. However, at the present, these methods generate a large amount of data that need trained professionals for interpretation and management. In addition molecular biology methods are still expensive and difficult to establish as a routinary diagnosis tool. Another possibility is the use of molecular biology in the biomonitoring of work environment. Biomonitoring is the way of recording and quantifying environmental and occupational loads. The selection of the biomonitoring parameter for a specific case must be based on the characteristics of the toxic effect of the foreign substance. Finally, computational or in silico, analyses contribute to evaluate occupational risk. Use of databases and predictive software may help to integrate multiple experimental data with algorithms and project potential risks in occupational environment. Despite the accuracy of molecular techniques, at present, majority of these methods are far from being routinary used in clinics mainly due to its cost. In addition, more research is needed to understand the association between exposure and disease development. It is widely known that environmental, lifestyle, nutritional and health status as well as genetic background (and even epigenetic factors) are involved in the development of pathological process. Therefore, exposure in the occupational environment, sometimes may act as the trigger for chronic illnesses. Yet, the more researchers, physicians and occupationally-exposed employees work together, share information, develop clinical studies and generate new data by using molecular biology methods, the more useful the results obtained. These facts, all together, are increasing the knowledge of the basis of disease development and its association with exposure in the work environment. Therefore, molecular biology methods have become useful, powerful tools to identify sensitive biomarkers and detect the earliest health outcomes in workers occupationally exposed to chemicals.