High performance liquid chromatography has detected 14 abnormal hematological states in 600 randomly selected samples of blood. Two of these are silent mutations which are not apparent from chromatographic or electrophoretic examination. One of these has the substitutionα76 (EF5) Met→Thr and has been named Hb Aztec. The variant was first detected in a 9-day-old baby girl who had inherited it from her mother. This abnormal hemoglobin has no obviously deleterious effect or hematological status or health.