The major macromolecules on the surface of the parasitic protozoan Leishmania major appear to be down-regulated during transformation of the parasite from an insect-dwelling promastigote stage to an intracellular amastigote stage that invades mammalian macrophages. In contrast, the major parasite glycolipids, the glycoinositol phospholipids (GIPLs), are shown here to be expressed at near-constant levels in both developmental stages. The structures of the GIPLs from tissue-derived amastigotes have been determined by h.p.l.c. analysis of the deaminated and reduced glycan head groups, and by chemical and enzymic sequencing. The deduced structures appear to form a complete biosynthetic series, ranging from Man alpha 1-4GlcN-phosphatidylinositol (PI) to Gal alpha 1-3Galf beta 1-3Man alpha 1-3Man alpha 1-4GlcN-PI (GIPL-2). A small proportion of GIPL-2 was further extended by addition of a Gal residue in either alpha 1-6 or beta 1-3 linkage. From g.c.-m.s. analysis and mild base treatment, all the GIPLs were shown to contain either alkylacylglycerol or lyso-alkylglycerol lipid moieties, where the alkyl chains were predominantly C18:0, with lower levels of C20:0, C22:0 and C24:0. L. major amastigotes also contained at least two PI-specific phospholipase C-resistant glycolipids which are absent from promastigotes. These neutral glycolipids were resistant to both mild acid and mild base hydrolysis, contained terminal beta-Gal residues and were not lost during extensive purification of amastigotes from host cell membranes. It is likely that these glycolipids are glycosphingolipids acquired from the mammalian host. The GIPL profile of L. major amastigotes is compared with the profiles found in L. major promastigotes and L. donovani amastigotes.