Assessment of occupational exposures is a crucial factor in evaluating dose-response relationships and most studies conducted by the Branch have an extensive exposure assessment component. Major assessment efforts in cohort studies have involved exposures to asbestos, organic solvents, pesticides, benzene, xylene, toluene, and diesel fumes. In the case-control design, jobs have been evaluated for a wide variety of exposures, including chlorinated hydrocarbons and other solvents, asbestos, formaldehyde, electromagnetic fields, physical activity, nitrosamines, polycyclic aromatic hydrocarbons, wood dust, diesel exhaust and pesticides. These exposures have been evaluated in studies of cancer of the peritoneum, breast, kidney, stomach, nasopharynx, esophagus, pancreas, brain, bladder, and lymphatic and hematopoietic system and for studies of parental occupation and childhood cancers. Methodologic studies are also conducted to improve exposure assessment techniques and to understand exposure patterns. A study is being initiated evaluating assessments made from detailed occupational questionnaires with air measurements. Comparison of jobs identified on death certificates is being made with work history records. Investigations were made on the reliability of industrial hygienists assessing exposures using written materials describing formaldehyde exposures and viewing a videotape of pesticide applications. In addition, a report describing how exposures to pesticides are being assessed in a large cohort study of pesticide appicators is being prepared. Two computer programs to assist in exposure assessment for cohort and for case-control studies are being developed. Two reviews of pesticide information available in the public arena provide guidance on how to assess exposures to migrant workers. A report describing the exposure assessment procedures in the Chinese benzene study was developed.