The role of exposure assessments in epidemiological studies was discussed. The purposes of exposure assessments were summarized. These included comparing existing exposures to those mandated by legal or recommended standards, evaluating the effects of changes in processes and control technology, and for epidemiological purposes in industrywide studies. Exposure assessments conducted in conjunction with industrywide studies are regarded as being very useful because they can be used to identify populations for health risk studies, to conduct risk assessments, or to reconstruct historical exposures. It was noted that when exposure measurements were linked to outcomes such as morbidity and mortality in epidemiological studies, exposure was being used as a surrogate of dose. Strategies for conducting exposure assessments for industrywide studies were discussed. The problem of evaluating potentially confounding exposures was considered. An example, characterizing which solvent exposures were important for painters, was given. The problem was solved by adopting a three tiered sampling strategy: taking bulk liquid samples of all paints used during the sampling period, conducting area air sampling based on the results obtained from the bulk liquid samples, and conducting personal air sampling of individual painters. The authors emphasize the need for careful cooperation between industrial hygienists and laboratory scientists.