1. Hemoglobin (Hb) of the river buffalo (Bubalus bubalis L.) was studied by employing isoelectric focusing (IEF) in the 6.7-7.7 pH range and by IEF in ultra-narrow immobilized pH gradient (IPG) 7.1-7.5. 2. Three Hb BB phenotypes were identified which were characterized by sets of two or four Hbs with different isoelectric points. 3. These type were called BB, BsBs and BBs, the Bs phenotype showing Hbs with slightly slower mobility. 4. Analysis of constituent globin chains by acid urea polyacrylamide gel electrophoresis in the presence of Triton X-100, provided clear evidence of a novel polymorphism at the beta-globin level. 5. Titration curves of beta-globins from heterozygous Hb BBs indicated a single curve thus suggesting the absence of a net charge in all the pH field. 6. A neutral-to-neutral amino acid replacement probably differentiates the two beta-globins.