Major advances in molecular biology during recent years have helped to identify genes and enzymes that play an important role in many diseases. While not ruling out traditional forms of epidemiology, the application of epidemiologic study designs in molecular biological studies may provide possibilities of disclosing disease mechanisms at the gene level and identifying more specific indicators of disease. Data on adducts to DNA or protein usually lead to cross-sectional studies or cohorts. Genetically determined susceptibility or mutations in tumor cells might be available and possibly reflect etiologically important determinants. The case-control design is applicable and cost-effective for the analysis of such data.