We report the precision of the mean migration position of hemoglobin (Hb)S, HbC, HbG (Philadelphia), and HbD (Los Angeles) in 193 samples of whole blood assayed by capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC). By expressing the migration of Hb variants by CE relative to that of HbA(2) in the same sample, there was a significant improvement in the coefficient of variation for each variant studied. The potential usefulness of expressing Hb variants relative to that of HbA(2) was evaluated by comparing the separation of 2 closely migrating Hbs. When expressed by their initial migrations on CE, 25 of the 43 cases of HbG and HbD overlapped. However, when the migrations of these variants were expressed relative to the HbA(2) in the same sample, the 24 cases of HbG separated completely from the 19 cases of HbD. These findings suggest that expressing Hb variants relative to an internal standard, such as HbA(2), may be of value for establishing a library of variant Hbs evaluated by CE.