Recent developments in analytical chemistry improve our ability to characterise individual exposure to environmental pollutants by measuring their levels in accessible biological media, down to the nanomolar level even for organic compounds. As useful complements for risk assessment, biomarkers of individual susceptibility are being intensively investigated in both cancer and non cancer epidemiology, acknowledging that host factors may not only play a key role in multifactorial diseases, but also affect the lower tail of the dose-response relationship for toxic outcomes. A third promising area of research is the development and validation of biomarkers of early effect. The use of more quantitative and sensitive end-points could increase our ability to identify toxic responses to chemicals polluting the workplace and the general environment. As a whole, these advances are likely to result in a better characterisation of dose-response relationships, a key step towards effective prevention. This paper provides an overview of the 4th International Symposium on Biological Monitoring.