The levels of glycogen, hyaluronic acid, chondroitin sulfates, N-acetylneuraminic acid, all of the monosaccharide components of the glycoprotein and glycolipid fractions, and the monosaccharide pools were measured in cultured chick embryo fibroblasts. Under all growth conditions, the glycogen plus the glucose phosphate pool contained approximately 50% of total monosaccharide content of the cells. However, marked qualitative and quantitative alterations were found in the glycoprotein, glycolipid, and mucopolysaccharide fractions when growing cells reached confluence, when the growth temperature was shifted from 36 to 41 degrees, or when the cells were transformed with Rous sarcoma virus. From 65 to 95% of the total monosaccharide residues in these complex carbohydrates were found in the glycoprotein fraction, while the glycolipids contained only 5 to 10% of the residues, and the mucopolysaccharides contained 5 to 25%. Changes in the complex carbohydrates in normal cells following changes in cell density or growth temperature were so great that they obscured any transformation-dependent changes that might have occurred consistently in the virus-infected cells under different growth conditions.