The study of the gene-environment interaction considered initially genes involved in the biotransformation of carcinogenic agents. Genetic polymorphisms are useful markers of individual susceptibility, provided that their association with the exposure and the outcome of interest are clearly understood. The availability of biochemical and molecular markers in epidemiology research has been greeted as a major step forward from the traditional "black box" epidemiology, and certainly represents a real advancement in knowledge. Yet, the advancement in research made possible by the adoption of molecular biomarkers in epidemiological studies still needs to be evaluated as a relevant and effective tool for a more adequate prevention of the adverse effects caused by environmental agents.