Dissociated 7-day chick embryo neural retina cells exhibited marked biosynthetic activity as measured by 14C-glucosamine and 3H-glycine incorporation. Glucosamine incorporation was more nearly directly related to the degree of aggregation than glycine incorporation. Several different labeled amino acids gave results very similar to glycine. Qualitatively, similar results were obtained using dissociated 7-day embryo liver and neural retina cells. Aggregation and incorporation of labeled glycine and glucosamine were inhibited by actinomycin D, puromycin, phleomycin, cycloheximide, borate, and periodate. Free hexosamines blocked aggregation and the incorporation of the amino acids and glucosamine by neural retina cells, but their acetylated derivatives and hexoses in similar concentrations did not. A number of amines, phenethyl alcohol, and EDTA depressed the incorporation of these precursors into macromolecules. Protein or some other macromolecules were required for maximal activity. Although the biosynthetic activity was dependent on the type of medium, all media showed an optimal protein concentration. Glycine predominantly labeled intracellular structures while glucosamine preferentially labeled the extracellular proteins. The distribution of the amino acid and glucosamine labels was dependent upon the protein concentration of the medium. Chick embryo extract was found unnecessary and occasionally inhibitory. When aggregates were dissociated the material liberated on dissociation had a greater specific activity than the whole aggregates. When the cells were fractionated into membranous and non-membanous components, the membrane material had a greater specific activity than the whole cells.