This paper is written in the context of our changing perception of the immunological system as a system with possible biological roles exceeding the prevailing view of a system concerned principally with the defense against external pathogens. The view discussed here relates the immunological system inextricably to the metabolism of iron, the circulation of the blood and the resolution of the evolutionary paradox created by oxygen and iron. Indirect evidence for this inextricable relationship between the two systems can be derived from the discrepancy between the theoretical quasi-impossibility of the existence of an iron deficiency state in the adult and the reality of the WHO numbers of people in the world with iron deficiency anemia. With the mounting evidence that TNF, IL-1, and T lymphocyte cytokines affect hemopoiesis and iron metabolism it is possible that the reported discrepancy is a reflection of that inextricable interdependence between the two systems in the face of infection. Further direct evidence for a relationship between T cell subset numbers and iron metabolism is presented from the results of a study of T cell populations in patients with hereditary hemochromatosis. The recent finding of a correlation between low CD8+ lymphocyte numbers, liver damage associated with HCV positivity and severity of iron overload in beta-thalassemia major patients (unpublished data of RW Grady, P. Giardina, M. Hilgartner) concludes this review.