We have determined the structural abnormality of a putative Hb E detected in an African-American family with no apparent Asian ancestry. The tryptic peptide map performed by high performance liquid chromatography showed that the electrophoretic variant was indeed Hb E [β26 (B8)Glu→Lys]. In addition, the tryptic map showed an abnormal peptide adjacent to theαT-6 peptide. The amino acid analysis and confirmatory restriction analysis of the DNA showed that a second mutation was also present, characterized by a substitution of arginine for lysine at residue 56 of the a chain. The variant is clinically silent and has been named Hb Port Huron for the city in Michigan where the family resides.