The binding of lipopolysaccharide (LPS, also known as bacterial endotoxin) to human hemoglobin is known to result in oxidation of hemoglobin to methemoglobin and hemichrome. We have investigated the effects of the LPSs from smooth and rough Escherichia coliandSalmonella minnesotaon the rate of oxidation of native oxyhemoglobin A0and hemoglobin cross-linked between thea-99 lysines.