We have studied the glycolipid composition of human cataractous lenses. Neutral and acidic lipid fractions were isolated by column chromatographies on DEAE-Sephadex and Iatrobeads. The neutral glycolipid fraction and acidic glycolipid fraction contained 0.6-0.9 micrograms of lipid-bound glucose (Glc) per mg of protein and 0.8-1.3 micrograms of lipid-bound sialic acid (NeuAc) per mg of protein, respectively. The neutral glycolipid fraction was found to contain LacCer (39.0% of total neutral glycolipids), Gb3 (16.2%), Gb4 (1.1%), nLc4 (5.0%), X (29.0%), and Y (9.2%). The acidic lipid fraction was found to contain mainly GM3 (33.1% of the total ganglioside fraction), GM1 (8.3%), LM1 (7.3%), GD1a (16.0%), and G (30.1%). The structures of neutral glycolipids X and Y and ganglioside G were elucidated by high performance thin-layer chromatography overlay method of glycolipids, gas-liquid chromatography, proton NMR spectrometry, and liquid secondary ion mass spectrometry as follows: 1) X, Gal beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-3Gal beta 1-4Glc beta 1-1'Cer, III3FucnLc4 (Lex); 2) Y, Gal beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-3Gal beta 1-4(Fuc alpha 1- 3)GlcNAc beta 1-3Gal beta 1-4Glc beta 1-1'Cer, V3FucIII3FucnLc6; and 3) G, NeuAc alpha 2-3Gal beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-3 Gal-beta 1-4Glc beta 1-1'Cer, IV3NeuAcIII3FucnLc4 (sialosyl-Le(x)). A minor neutral glycolipid Z was isolated and tentatively characterized as GlcNAc beta 1-3?Gal beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-3Gal beta 1-4Glc beta 1-1'Cer (GlcNAc-Le(x)), suggesting that it may be the precursor of glycolipid Y. The major long-chain base of these human cataract glycolipids was C18:0 sphingosine (sphinganine). The major fatty acids were C16:0, C24:1 and C24:0, and monounsaturated fatty acids accounted for 40-55% of the total fatty acids.