The adhesive properties of cell surfaces which seem to determine many morphogenetic processes1 and which may be important in malignancy2 must reflect the biochemical characteristics of the cell surfaces. There have been attempts to isolate the macromolecules concerned by assaying for substances required for cell adhesion3, and one of us4 has described a promising experimental system for such studies. Trypsin-dissociated cells from an ascites-grown form of a mouse teratoma (teratocarcinoma, embryonal carcinoma)5,6 require L-glutamine in order to synthesize amino-sugars and to reaggregate in a solution of glucose and balanced salts, most probably because the amino-sugars are necessary for the formation of the complex carbohydrates involved in cell adhesion4. This communication describes experiments in which the amino-sugars are replaced by macromolecular substances in the ascites fluid in which the teratoma grew.