From 81 of human plasma of blood-group A Lea nonsecretors three different Lea blood-group active ceramide pentasaccharides (a total of 4.65 mg) have been isolated, all revealing glucose, galactose, N-acetylglucosamine and fucose in molar ratios of 1 : 2 : 1 : 1 as determined by gas liquid chromatography. A fourth blood-group active fraction (0.72 mg) represents a mixture of a Lea active ceramide pentasaccharide and an A active ceramide hexasaccharide (molar ration 7.7 : 2.3 as calculated from the content of different aminosugars). Additionally, two different globosides, two different hematosides and a new N-acetylglucosamine containing ceramide tetrasaccharide were obtained. All 9 glycolipid fractions demonstrated homogeneity in analytical high performance thin layer chromatography (HPTLC) using 4 different solvent systems. 0.2 microgram of each Lea active glycolipid completely inhibited the agglutination of O Le(a+b-) erythrocytes by 50 microliter of 4 hemagglutinating units of caprine anti Lea serum. At least 0.04 microgram of each Lea antigen are sufficient for incubation to convert 9 x 10(7) O Le(a-b-) erythrocytes into Lea-positive cells. Mainly due to the relatively low content of the blood-group A glycolipid in plasma (0.17 mg/81), previously negative erythrocytes readily become agglutinable by anti Lea sera and not by anti A sera after incubation with appropriate plasma.