The minor hemoglobin components, hemoglobin AIa+b and hemoglobin AIc, were measured in the 10% youngest and 10% oldest erythrocytes of 15 normal and 14 diabetic subjects. Erythrocyte fractions were obtained by centrifugation in isopyknic concentrations of dextran: 28.5% of 40,000-mol wt dextran yeilded the 10% lightest of young cells, and 30.5% dextran provided the 10% heaviest or old erythrocytes. Both normal and diabetic erythrocytes contain increased amounts of Hb AIa+b and Hb AIc in old as compared to young cells. In normal subjects, young cells contained 1.2+/-0.2%, and old cells contained 1.8+/-0.4% Hb AIa+b. Corresponding values for diabetic cells were 1.7+/-0.6 and 2.6+/-0.9%. Hb AIc increased from 3.1+/-0.8 to 6.0+/-1.1% in normals and from 5.1+/-2.1 to 10.1+/-3.7% in diabetics. The results indicate that both cell age and diabetes are significant determinants of the amounts of Hb AIa+b and Hb AIc.