A review of recent studies of biologic markers in populations with model exposures to carcinogens (cigarette smoke and polycyclic aromatic hydrocarbons) illustrates their potential role in cancer prevention. Data on macromolecular adducts and oncogene activation from cross-sectional, serial sampling and case-control studies demonstrate the usefulness of biologic markers in signalling a potential carcinogenic risk and in estimating the magnitude of interindividual variation within exposed groups. Recommendations for future research include nested case-control studies to establish the relationship between markers of biologic dose and effect (e.g., adducts, gene mutation, oncogene activation) and cancer risk.