The importance of iron deficiency as a public health problem is based ultimately on the seriousness of its consequences on health. The most extensively investigated consequences of iron deficiency involve work performance and immune function. The significance of the effects on work performance are generally accepted. In contrast, data on the influence of iron deficiency on immune function are often perceived as being confusing and contradictory. From reexamination of relevant literature, it seems safe to conclude that abnormalities in cell-mediated immunity and ability of neutrophils to kill several types of bacteria are well established under experimental conditions in iron-deficient patients. It remains uncertain whether these abnormalities result in an increased incidence and duration of infections. This area still requires careful study.