In order to assess the issue of inequity in exposure to environmental hazards, researchers must identify subgroups whose exposure is disproportionately greater than the average exposure experienced by the remainder of the population. The general population is a complex mixture of subgroups, each consisting of individuals who experience a wide range of exposures and whose ability to cope with the consequences of those exposures is equally varied. Therefore, large efforts are needed to collect data that will enable researchers to determine comprehensively which subgroups are highly exposed and which subgroups have disproportionately greater health effects as a result of exposures to environmental hazards. The interpretation of findings is more of an art than a science, especially when two population subgroups are being contrasted. Addressing environmental equity requires explicit comparisons between groups, and racial and ethnic contrasts will be prominent. It is often difficult to identify the underlying mechanisms that produce particular patterns of results. However, researchers and policy makers must understand the dynamics that may have produced a particular pattern of results so they can separate those factors that are amenable to change from those that are not.