In a homogeneous immunoassay, fluorophore-conjugated lipopolysaccharide derived bacterial antigens are reacted with antibodies specific for the antigens. Quantitative detection of the formation of an immune complex is obtained by measuring the change in fluorescence polarization after complex formation. The reaction occurs quickly (less than two minutes to equilibrium), and involves the addition of only one reagent to a diluted serum specimen. The absence of a solid phase separation step eliminates false positive results and increases throughput.