Molecular epidemiology.

The use of biomarkers in epidemiology is not new, but recent developments in molecular biology and genetics have increased the opportunities for their use. However, epidemiological studies based on biomarkers, which belong to the discipline defined as 'molecular epidemiology' are subject to the same problems of design and analysis as 'traditional' epidemiological studies. If biomarkers offer new opportunities to overcome some of the limitations of epidemiology, their added value over traditional approaches should be systematically assessed. Biomarkers should be validated though transitional studies; consideration to sources of bias and confounding in molecular epidemiology studies should be no less stringent than in traditional studies.