The main focus of the discipline of immunotoxicology is the study of alterations in immunological mechanisms caused by chemicals and drugs. These alterations may result in increased incidence of infections or the development of tumors. The major interest of immunotoxicology lies in the evaluation of the results of toxicity testing in rodents for the purpose of risk assessment for humans. As J. G. Vos and colleagues explain, such immunotoxicity testing is preferably carried out as a tiered system consisting of screening followed by functional studies of selected chemicals. This approach has been successful in identifying notorious environmental pollutants as immunotoxic chemicals. Evidence that the non-mammalian immune system can also be damaged by toxic environmental pollutants emphasizes the importance of ecotoxicology.