AbstractA silent β‐chain hemoglobin variant, not detectable by starch gel or agar gel electrophoresis was found using Triton X‐100 acid‐urea polyacrylamide gel electrophoresis. The abnormal β‐X chain had a more anodic electrophoretic mobility; 38% of the total β chain was of the abnormal type. Structural analysis using high‐performance liquid chromatography and microsequencing procedures indicated a valine to isoleucine substitution at position β11(A8). This anomaly did not change the functional proper ties of the hemoglobin molecule. A mild reticulocytosis was observed in t