Hb Detroit is a mutant which migrates between Hb A and Hb J Baltimore on cellulose acetate (pH 8.5), and with Hb A on citrate agar (pH 6.0). Globin chain analyses in alkaline and acid buffers reveal an abnormal beta chain with a mobility between the betaA and betaJ Baltimore chains. Structural characterization of this abnormal chain shows that lysine at position 95 is replaced by asparagine. No hematological abnormalities could be attributed to the presence of the mutant, and the oxygen affinity properties of the stripped hemoglobin are similar to those of Hb A. The beta95 residue which is substituted in Hb Detroit and also in Hb N Baltimore ((beta95 Lys leads to Glu) does not appear to be in a critical functional area of the molecule.