Rabbit antisera directed against human milk sialyloligosaccharides were used to detect specific monosialylgangliosides from the lipid fraction of human meconium. Gangliosides of this fraction were detected after thin layer chromatography by immuno-staining with specific anti-oligosaccharide sera. The monosialylganglioside fraction of human meconium was subjected to ozonolysis and alkali-fragmentation and the resulting ganglioside-derived oligosaccharides were reduced with NaB [³H]₄ and partially separated using paper chromatography. The [³H]-oligosaccharide alditols were assayed for binding to specific anti-oligosaccharide sera in a direct-binding radioimmunoassay using nitrocellulose filters to collect immune-complexes. Radiolabeled oligosaccharide alditols which were recognized by specific antisera were affinity purified by eluting nitrocelIulose filters containing antibody-oligosaccharide complexes or using columns of immobilized anti-oligosaccharide antibodies. Structural analyses of two sialyl[³H]tetrasaccharide alditols obtained in this way were carried out with sequential enzymatic degradation using specific exoglycosidases. The products of enzymatic digestions were identified by cochromatography in paper with known standards. Data obtained from these experiments are consistent with the presence of the following, previously unidentified gangliosides in human meconium: NeuAcα2-3Galβ1-3GlcNAcβ1-3Galβ1-4Glc-cer Galβ1-3[NeuAcα2-6]GlcNAcα1-3Galβ1-4Glc-cer / Ph. D.