agents or tumor cells. Animal studies, primarily those which use rodents, have provided a large information base about potentially immunotoxic chemicals, suggestive evidence of the mechanisms for their effects, and an appreciation that the immune system is susceptible to chemical injury. The susceptibility of the immune system is due as much to the general properties of a chemical (e.g., its reactivity to macromolecules) as it is to the complex nature of the immune system. Because the cellular events responsible for immune processes also are involved in embryogenesis, many immunosuppressive xenobiotics would be expected to be developmental toxicants.

To date, animal data have not been used to any significant extent in the assessment of human risk resulting from exposure to immunosuppressive environmental pollutants. Extrapolating short-term, high-dose animal studies to chronic low-dose human exposure