It has been purported that Gulf War Syndrome patients who were vaccinated prior to deployment exhibited antibodies to squalene (SQE) and that these antibodies to SQE were not observed in normal humans (Asa et al., 2000). Further study has shown that monoclonal antibodies (mAbs) to SQE are produced by immunization of mice with formulations containing SQE (Matyas et al., 2000). However, the exact specificities of the mAbs to SQE have not been described. An enzyme-linked immunosorbent assay (ELISA) is described here to measure the binding of SQE mAbs to lipid antigens. SQE is a biosynthetic precursor to cholesterol, and the majority of the mAbs reacted with cholesterol. The mAbs reacted with Lipid A and with squalane (hydrogenated SQE) to a lesser extent. Some of the mAbs reacted strongly with dimyristoyl phosphatidylcholine (DMPC), though exhibited weak reactivity with dimyristoyl phosphatidylglycerol (DMPG). All of the mAbs cross-reacted with at least one lipid antigen other than SQE. This suggests that antibodies to other lipids may also cross-react with SQE. Since Asa et al. (2000) did not assay for antibodies to other lipids, their purported anti-SQE activity may be antibodies to other lipids which have been shown to occur in humans with autoimmune diseases (Meager et al., 1999).