Criteria for determining the occupational groups and operations which constituted heavy asbestos (1332214) exposure were derived from workers' compensation cases involving asbestosis, silico/asbestosis, mesothelioma, and lung cancer in Western Australia. Problems in attempts to uncover relationships between occupational groups and the heaviness of asbestos exposure included selection bias, recall bias, the possibility of multiple exposures, the problem of intermittent exposure, and incomplete descriptions of jobs and duration of exposure to asbestos. Heaviness of asbestos exposure was described as the product of intensity and duration. In determining the intensity of asbestos exposure in the absence of direct dust exposure measurements, an accurate description of the job was required to obtain an indirect indication of intensity. The description could be partially corroborated by a knowledge of claimants who did similar jobs. The authors conclude that it is important to take into account the type of asbestos, the intensity of exposure, and the duration of exposure in any analysis of asbestos induced occupational lung disease.