Structures of the major glycolipids isolated from the protozoan parasite Leishmania major (strains V121 and LRC-L119), were elucidated by fast atom bombardment-mass spectrometry, two-dimensional proton NMR, methylation analysis, exoglycosidase digestions and mild acid hydrolysis. These glycolipids belong to a family of glycoinositolphospholipids (GIPLs), which contain 4-6 saccharide residues linked to alkylacylphosphatidylinositol (alkylacyl-PI) or lyso alkyl-PI. The general structure of the elucidated GIPLs can be expressed as follows: R-3Galf(alpha 1-3)Manp(alpha 1-3)Manp(alpha 1-4)GlcNp(alpha 1-6) alkylacyl-PI or lyso alkyl-PI where R = OH for GIPL-1; R = Galp(alpha 1- for GIPL-2; R = Galp(alpha 1-6)Galp (alpha 1- for GIPL-3 and R = Galp(alpha 1-3)Galf(alpha 1- for GIPL-A. The alkylacyl-PI lipid moieties are unusual in containing predominantly 18:0, 22:0, 24:0, or 26:0 alkyl chains and 12:0, 14:0, or 16:0 acyl chains. Remodeling of the lipid moieties may occur based on the finding that 1) lyso derivatives account for approximately 35% of the GIPL-3 fraction in strain V121 and 2) there is an increase in the proportion of 24:0 and 26:0 alkyl chains with elongation of the carbohydrate chain. Together with the elucidated structures, these properties are consistent with some of the GIPLs having a role as biosynthetic precursors to the major cell surface glycoconjugate, lipophosphoglycan. In particular, the saccharide sequences of GIPL-3, lyso-GIPL-3, and the glycan core of lipophosphoglycan (Turco, S. J., Orlandi, P. A., Homans, S. W., Ferguson, M. A. J., Dwek, R. A., and Rademacher, T. W. (1989) J. Biol. Chem. 264, 6711-6715) are identical. Finally, immunostaining of thin layer chromatograms with antibodies from patients with cutaneous leishmaniasis suggests that the major GIPLs are highly immunogenic and that the elevated anti-Gal antibodies, commonly seen in leishmaniasis patients, may be directed against terminal Galp(alpha 1-3)Galf residues.