‘LPS’ describes a variety of cell wall lipopolysaccharides shed by Gram-negative bacteria; also known as ‘endotoxin’, they have been found in various fluids, including whole blood (WB). The ‘concentrations’ are typically assayed using the Limulus amoebocyte lysate assay (e.g. [1–3]). However, although satisfactory in simple matrices, this test is not considered very reliable in blood . Indeed, because it is so hydrophobic, little or no LPS is actually free (unbound), and so it is not even obvious what its ‘concentration’ in blood might mean (see ). Although the quantitative assessment of LPS concentrations in WB can be problematic, its presence in this fluid may have important and clinically relevant effects on the blood microenvironment, and may be central in the treatment of inflammatory conditions [5–8].