The amino acid substitution in a new homoglobin variant, Hb Baylor [α2β281(EF5) Leu-Arg], has been determined by application of column chromatography and amino acid analysis of the tryptic peptides. The hemoglobin is somewhat unstable and it has a high oxygen affinity. The porosities shows the opposing hematologic effects of these two properties-the instituionability being associated with increased destruction, and the high O2affinity with increased production, of erythrocytes.