By chromatographic methods, it has been shown that both crystallized and uncrystallized normal adult human hemoglobin contain a main component that comprises about 90% of the heme proteins. Three minor heme proteins and a non-heme protein also have been detected. The several components are not artifacts of preparation or chromatography, and they have been shown to differ in their content of isoleucine. Cord blood hemoglobin also contains minor components. These results are discussed in relation to other reports of the heterogeneity of human hemoglobin. The methods described may be used for the isolation of preparative amounts of the main components.