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Experiments were performed to characterize the accumulation of different exogenous sialoglycolipids by cells.A biphasic kinetics of accumulation appeared to be characteristic for intact primary and permanent monolayer cells and chicken erythrocytes whereas that of chicken erythrocyte ghosts was monophasic. Saturation levels could be reached with Galbl+3 GalNAcpl+4 Gal[3+2aNeuAc]-, !I1 +4 GlcPl -1'Cer and Galfil-+3 GalNAcfil -4 Ga1[3c2aNeuAc8+2aNeuAc]fil+4 Glc@ -1'Cer with concentrations of 100 and 200 nmol per ml culture medium, respectively. Under these conditions the amount of 1.3 -1.4 nmol of sialoglycolipids per 100 pg of cellular protein were found to be cell-bound after approximately two hours. In case of the ganglioside NeuAccr2+3GalfiI -4Glcfll -1'Cer no saturation could be reached.The intermediate plateau of accumulation was abolished by the agents colchicine and sodium fluoride which on the other hand had no influence on the level of saturation. In contrast the presence of cytochalasin B, 2-deoxy-~-glucose plus sodium azide, and glutardialdehyde as well as low temperature decreased the amount of incorporated gangliosides drastically. The effect of cytochalasin B was limited to monolayer cultures.Mild trypsinisation liberated some 70 -85 % of cell-associated gangliosides even after druginhibited accumulation of gangliosides. Also some 87 -95 % of the cell-bound ganglioside NeuAca2+3 Galpl -4 Glcpl -1'Cer remained accessible to the action of exogenous sialidase, thus excluding gross internalisation Over the last several years reports have been accumulating that glycosphingolipids as constituents of the outer surface of mammalian cell membranes significantly contribute by means of their carbohydrate structures to a variety of cellular events. Since glycolipids are taken up by cells from the culture medium, attempts were reported to supplement surface membrane glycolipids by incorporation of exogenous compounds [I]. Glycolipid uptake was accompanied by a reduction in growth rate and saturation density [2-61.Abbreviations. Abbreviations were used according to principles outlined earlier Wiegandt, H. (1973) Hoppe-Seyler's Z . Physiol. Chetn. 354, 3049-1056. The first name given is that used in the text (for simplification the term NeuAc has been deleted in the text), the third name is designated as recommended by IUPAC-IUB Lipid Nomenclature, 1976, the final designation is according to Svennerholm (1963) J . Neurochem. 10, 613-623. GL,,lNeuAc = (I13NeuAc-Lac-Cer) = NeuAcct2-3 Gdlpl -t4 Glc,!?l-1'Cer = GM3; GGtetlNeuAc = (I13NeuAc-CgOse4-Cer) = Galp1+3 GalNAcfil-4 Gdl[3t2aNeuAc]fi1+4 GlcPl -1'Cer = GMl; Gct,,2b-NeuAc = I13(NeuAc)z-GgOse4-Cer = Galpl-3 GalNAcPl-4 Gal[3+2aNeuAc8t2aNeuAc]pl+4 Glcpl-1'Cer = GDlh.Enzymes. Trypsin (EC 3.4.21.4); galactose oxidase or D-galactose: oxygen 6-oxidoreductase (EC 1.1.3.9).

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