In summary, data from animal models would suggest that air measurements of substances can be correlated with immune response, be it immunodepression or either of the two forms of immunostimulation-autoantibody formation or specific immunologic sensitization. However, became immunodepression and autoantibody formation are not specific for a given substance, and because they can be induced by a variety of other factors such as drugs and intercurrent viral infections, it would seem unlikely that correlations between air measurements and measurements of immunodepression or autoantibody formation could be very useful. In contrast, specific immunologic sensitization is a response that can only be induced by exposure to a specific agent. The major problem confronting investigators attempting to perform concentration-response studies in humans is accurate measurement of workplace exposures. If exposures could be reliably quantified, it is likely that concentration-response correlations could be determined for worker groups. This could prove useful for estimating exposure of groups based on aggregate immune response. It would be most useful, however, for determining threshold concentrations below which a very low proportion of workers--perhaps 1 in 100 or even 1 in 1000--would become sensitized. These threshold concentration levels of sensitizing substances could be used to develop permissible exposure levels in the workplace. Reducing workplace sensitization and diseases such as occupational asthma and hypersensitivity pneumonitis would be of obvious benefit to workers, management, government, and society at large.