The haemoglobins of the adult domestic fowl were resolved by cation-exchange chromatography into two distinct components (designated Hb I and Hb II) in a ratio about 3 : 1. A third minor acidic component, Hb III, representing only 1 % of the total was also present. Hb I and Hb II and each of their globin subunits (0:1, pI; o:II, PII) were subjected to amino acid analysis. As reported by other workers, Hb II was found to have more of the dicarboxylic amino acids and less of the dibasic amino acids than Hb 1.