Measurements of oxygen binding to bovine hemoglobin have been carried out over the temperature range 15-37 degrees C at pH 7.33. The standard enthalpy of oxygenation after correction for the heat of oxygen solution and of the Bohr protons is found to be -7.1 or -7.2 kcal/mol in the presence of 0.1 M chloride or bromide, respectively. This value is well below the -14.4 kcal/mol determined for human hemoglobin under identical experimental conditions. As reported by Fronticelli et al. (C. Fronticelli, E. Bucci and A. Razynska, J. Mol. Biol. 202 (1988) 343), the preferential binding of anions by bovine hemoglobin recognizes the various halides. Measurements at various temperatures reveal that this is true only above 25 degrees C. The halide recognition and the less exothermic enthalpy of oxygenation of bovine hemoglobin are probable due to oxygen-linked hydrophobic effects that are larger in bovine than in human hemoglobin.