From 81 of human plasma of blood-group A Le a nonsecretors three different Le a 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 ola Le a active ceramide pentasaccharide and an A active ceramide hexasacchadde (molar ratio 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 tetrasacehaxide were obtained. All 9 glycolipid fractions demonstrated homogeneity in analytical high performance thin layer chromatography (HPTLC) using 4 different solvent systems. 0.2 vg of each Le a active glycolipid completely inhibited the agglutination of O Le(a + b-) erythrocytes by 50 ~1 of 4 hemagglutinating units of caprine anti Le a serum. At least 0.04 vg of each Le a antigen axe sufficient for incubation to convert 9 X i 0 ~ 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 Le a sera and not by anti A sera after incubation with appropriate plasma.