Lipopolysacharide (LPS) Binding Protein (LBP) is a type 1 acute phase protein that is constitutively produced by the liver and rapidly upregulated during the acute phase response. LBP plays a central role in the response to LPS. The protein catalyses the monomerization of LPS and its transfer to (s)CD14 and to lipoproteins. In this way LBP has both a role in the activation pathway of LPS: activation of monocytes by LPS leading to release of inflammatory mediators and in the neutralization of LPS i.e. the uptake of LPS by lipoprotein and subsequent clearing. The assay can be used to quantify functional LBP in tissue culture supernatants of cell cultures, plasma and serum samples of several species. In plasma of healthy individuals LBP is present at levels which increase during acute phase responses.