The standard in-vitro assay used to test for endotoxin presence, much preferred over the in-vivo rabbit pyrogen test. LAL is an aqueous extract of blood cells (amoebocytes) from the horseshoe crab, Limulus polyphemus. LAL reacts with bacterial endotoxin or lipopolysaccharide (LPS), which is a membrane component of Gram negative bacteria. This reaction is the basis of the LAL test, which is used for the detection and quantification of bacterial endotoxins.