Rabbit antibodies against human milk sialyltetrasaccharide b Galßl—3[NeuAca2—6]GlcNAcßl—3Galßl—4Glc) and sialyltetrasaccharide a (NeuAca2-3Ga|ßl·3GlcNAcß1-3Galßl-4Glc) were used to detect their homologous haptens as gangliosides in the human colorectal carcinoma cell line SW'lll6. Sialyltetrasaccharide b-ceramide was detected in the monosialylganglioside fraction from human meconium and a total ganglioside fraction from SWlll6 cells on thin layer chromatograms by radioimmune staining using anti-sialyltetrasaccharide . b. Sialyltetrasaccharide b-ceramide was not detected in a total Iipid extract from normal intestinal mucosa, thus suggesting that it may represent another tumor·associated antigen. Two novel disialylgangliosides recently reported in human colonic adenocarcinoma — disialylIactotetraosylceramide (NeuAc¤2·3Ga|ß1-3[NeuAca2·6]GlcNAcßl-3 Galßl-4Glcl-lCer) and disialyl Lea (NeuAc¤2-3Ga|B1—3[NeuAc¤2-6 (Fucal·4)]GIcNAcßl-3Ga|ßl-4Glcl·lCer) -· both contain the sialyltetrasaccharide a and b structures, either of which may represent the biosynthetic precursor of these disialylgangliosides. The anti·sialy|tetrasaccharide a antibody specifically recognizes its reduced homologous hapten and was used in a radioimmmune binding assay to detect sialyltetrasaccharide a as a reduced and tritiated, ganglioside·derived sialyloligosaccharide from SWlll6 cells. Sialyltetrasaccharide a-ceramide was recently detected in human embryonal carcinoma cells, and it is the biosynthetic precursor of the sialyl Lea antigen, a tumor-associated ganglioside in SWH16 cells. This report confirms the existence of sialyltetrasaccharide a-ceramide in SW11l6 cells.