The HemoCue system measures the hemoglobin level in undiluted capillary or venous blood after conversion of hemoglobin to azide methemoglobin. The authors have compared this system, designed primarily for office use, with the Coulter S-Plus III in a study of 200 than or equal to 105 g/L (10.5 g/dL) and 47 children with sickle cell disease. The HemoCue system yielded values similar to those of the Coulter S-Plus III for nonanemic patients (mean difference 3.5 g/L [0.35 g/dL]; limits of agreement -6.7-13.7 g/L [-0.67-1.37 g/dL]) as well as for anemic patients (mean difference 3.3 g/L [0.33 g/dL]; limits of agreement -4.7-11.3 g/L [-0.47-1.13 g/dL]) and patients with sickling disorders (mean difference 4.2 g/L [0.42 g/dL]; limits of agreement -5.6-14.0 g/L [-0.56-1.40 g/dL]). Discrepancies of more than 10 g/L (1.0 g/dL) occurred in 13 of 200 measurements (6%); the HemoCue system gave the lower reading in all instances. The HemoCue system is comparable to standard laboratory techniques for measurement of hemoglobin level in normal and anemic children and is well suited for use in the outpatient care of healthy pediatric patients as well as those with hematologic disorders.