The study of interactions between genes and environmental exposures has expanded considerably in recent years. Highly penetrant genes that are involved in familial cancer have been identified, but are likely to account for a relatively small proportion of total cancers. Other predisposing genes have low penetrance, resulting in a moderate increase in the risk of specific cancers, but are widespread in the general population. This is the case for so-called metabolic polymorphisms. Scientific interest in metabolic polymorphisms is based on the possibility of identifying subgroups of the population which are at elevated risk of developing environmentally-induced cancer. However, such studies raise a series of problems that are methodological - related to the study design and analysis - and ethical - related to the practical use that can be made of genetic information. This volume deals thoroughly with such problems.