The phenomenon of aggregation of chick embryo cells in vitro has been investigated by the rotation-mediated cell-aggregation procedure. In serum-supplemented media trypsin-dissociated neural-retina cells and EDTA-dissociated cells produced aggregates which appeared very similar in size and form. Drugs which are known to interfere with macromolecular synthesis, and which prevent the formation of rotation-mediated aggregates by trypsinized cells appear to be less effective in inhibiting the aggregation of EDTA dissociated cells. The aggregation of EDTA-dissociated cells does not appear to be affected by periodate or by borate at concentrations that significantly inhibit the aggregation of trypsin-dissociated cells. The aggregation of both EDTA-dissociated and trypsin-dissociated retina and liver cells is greatly inhibited by 0.5 per cent glucosamine; however, numerous other aminosugars and other organic amines will cause a similar inhibition at concentrations of 0.5 per cent or less. © 1968.