In order to validate a number of biologic markers as indicators of effective dose or potential risk, we have applied them in related cross-sectional, longitudinal and case-control studies. Biologic markers such as carcinogen-DNA adducts and activated oncogenes have already provided insights into mechanisms of chemical carcinogenesis. They have also given information regarding the extent of interindividual variation in biologic response within the human population. These results are directly relevant to quantitative risk assessment. However, more research is needed to establish quantitative links between biologic markers and human risk of cancer.