An observation was made that patients with iron deficiency anemia rarely succumb to infections, whereas those with sickle cell anemia frequently do. To substantiate this, equal volumes of blood from 12 patients with severe iron deficiency anemia (mean hemoglobin 3.3 Gm. per 100 ml.), eight patients with sickle cell anemia (homozygous sickle cell disease) (mean hemoglobin 3.4 Gm. per 100 ml.), and l4 normal control subjects (mean hemoglobin 14.3 Gm. per 100 ml.) were studied for their capacity to support bacterial growth. The specimens were incubated in vitro with fixed volumes of Staphylococcus albus suspension for 18 hr. at 37 C., and then plated on blood agar and reincubated for 24 hr. at the same temperature. Each step was carefully controlled. The specimens from patients with iron deficiency anemia (except the two patients who also had kwashiorkor) grew fewer organisms than did the specimens from normal control subjects. However, the specimens from patients with sickle cell anemia (except the two patients with superimposed iron deficiency) yielded more colonies than the control. The results are discussed.