To demonstrate the importance of bone marrow iron stores, we examined the complete hemogram, serum iron (SI), serum iron-binding capacity (SIBC), transferrin saturation (TS), serum ferritin and bone-marrow-stored iron in 31 children with iron deficiency (ID). The ages of the patients ranged from one to 14 years (mean 3.7 +/- 3.9). Laboratory findings of the 31 patients were as follows: hemoglobin (Hb) 8.5 +/- 2.4 g/dl, hematocrit (Hct) 27.8 +/- 6.3 percent, mean corpuscular volume (MCV) 58.6 +/- 8.6 fl, red blood cell count (RBC) 4 +/- 0.8 10(12)/L, red cell distribution width (RDW) 19.3 +/- 4.9, SI 17.2 +/- 9.3 microg/dl, SIBC 311 +/- 50.5 microg/dl, TS 5.5 +/- 2.8 percent and ferritin 6.7 +/- 7.3 ng/dl. In the bone marrow smears with iron stains, all patients' scores were zero for iron stores, which shows that bone-marrow-stored iron in childhood is easily affected. Because of the traumatic effect of bone marrow aspiration, it is recommended that it not be done routinely. The diagnosis of ID could be especially difficult in patients with low SI levels but normal SIBC levels and in patients with chronic inflammatory diseases. In those conditions, illustration of bone marrow stores could be of particular assistance for diagnosis of iron deficiency.