The major cell surface glycoconjugate of Leishmania major, a putative parasite receptor for macrophages, is a lipophosphoglycan containing 81.6% (wt/wt) carbohydrate, 17.0% (wt/wt) phosphate, and 1.4% (wt/wt) lipid. It has been purified to homogeneity by hydrophobic chromatography and consists of a polydisperse family of molecules with Mr 5000-40,000. It contains galactose, mannose, glucose, arabinose, glucosamine, and inositol in the molar ratio of 51:21:5:6:1:1. The lipophosphoglycan has a complex structure, consisting mainly of tri- and tetrasaccharide units linked by phosphodiester bonds, which are cleaved by HF hydrolysis. The phosphate groups are located on the 6-hydroxyl of both galactose and mannose residues. The lipophosphoglycan is anchored to the parasite surface by a 1-O-alkyl-sn-glycero-3-phosphoinositol moiety. This conclusion is supported by analysis of the products of nitrous acid deamination, HF hydrolysis, and Staphylococcus aureus phosphatidylinositol specific-phospholipase C treatment. The 24:0 and 26:0 alkyl chains accounted for 93% of the ether-linked fatty acids in the lipid anchor. The results are also consistent with a glycosidic linkage between the inositol and a non-N-acetylated glucosamine residue. The lipophosphoglycan membrane anchor shares limited structural homology with the glycosylphosphatidylinositol anchors of several eukaryotic proteins, indicating that this type of membrane anchor is not limited to proteins. Vaccination of mice with the purified L. major lipophosphoglycan in liposomes induced resistance against cutaneous leishmaniasis.