Total non-acid glycosphingolipids were isolated from the plasma of a healthy red blood cell group O Le(a-b-) salivary ABH secretor individual. Glycolipids were fractionated by HPLC and combined into eight fractions based on chromatographic and immunoreactive properties. These glycolipid fractions were analysed by thin-layer chromatography and tested for Lewis activity with antibodies reactive to the type 1 precursor (Le(c)), H type 1 (Le(d)), Le(a) and Le(b) epitopes. Fractions were structurally characterized by mass spectrometry (EI-MS and LSIMS) and proton NMR spectroscopy. Expected blood group glycolipids, such as H type 1, (Fuc alpha 1-2Gal beta 1-3GlcNac beta 1-3Gal beta 1-4Glc beta 1-1Cer) were immunochemically and structurally identified. Inconsistent with the red cell phenotype and for the first time, small quantities of Le(b) blood group glycolipids (Fuc alpha 1-2Gal beta 1-3(Fuc alpha 1-4)GlcNAc beta 1-4Glc beta 1-1Cer) were immunochemically and structurally identified in the plasma of a Lewis-negative individual. These findings confirm recent immunological evidence suggesting the production of small amounts of Lewis antigens by Lewis negative individuals.