A method was developed to obtain antibodies to endotoxins. The method utilized the recognized binding ability of polymyxin B for lipopolysaccharide (LPS). E. Coli 055:85 LPS was mixed with polymyxin B-immobilized on agarose. When emulsified with Freund's adjuvant and injected into guinea pigs, the immnunogen stimulated the production of high titer antisera specific for the LPS moiety. Antibodies to the polymyxin B carrier were not detected. This procedure offers great promise as a method to produce LPS-specific antisera in high titer for use in detecting endotoxin in complex biological materials.