A variety of immunological responses has been associated with occupational lung disease and thus they may be involved in some aspects of pathogenesis. Genetic factors may also play a role in the development of occupational lung disease. A further inherited variable which may affect the response of individuals to dust exposure is their histocompatibility antigen type (HLA). While there may be some evidence of altered immune response in those dust-exposed workers who develop lung disease, these changes do not occur in every worker so exposed. The following series of studies was thus devised to investigate various aspects of individual susceptibility that might be important in the development of lung disease following exposure to coal dust.