A precise and reproducible method for assessment of glycated hemoglobin in human adult red blood cells is reported, based on capillary isoelectric focusing (IEF). In order to obtan baseline resolution between adult hemoglobin (Hb A) and its glycated form (Hb A1c), two species which differ by minute ΔpI values, < 0.03 pH units, the following procedure was adopted: the focusing mixture consisted of 5% Ampholine, pH 6–8, 0.5% Pharmalyte, pH 3–10, 3% short-chain liquid polyacrylamide and an equimolar mixture of two “separators”, 0.33 M β-alanine and 0.33 M 6-aminocaproic acid. The last two compounds flatten the pH gradient in the pI region of the two Hbs, thus allowing full separation. Additionally, the Hb samples, instead of being pulse-loaded, are uniformly distributed in the background electrolyte. A longer capillary lifetime is obtained if all nonbuffering ions are eliminated; thus, as catholyte, 50 mM Lys (pH 9.7) is utilized and as anolyte 50 mM acetic acid (pH 3.5) is adopted. The percentages of Hb A1c, as obtained by capillary IEF, are in good agreement (±6%) with data obtained by one of the standard zone electrophoretic methods in clinical chemistry, i.e., the Helena REP Glyco gel system.