Plasma membranes were isolated from an ascites hepatoma, AH 66, after the cells had been hardened by treatment with fluorescein mercuric acetate (FMA) or Zn ions. The carbohydrate compositions of these plasma membrane preparations, FMA- and Zn-membranes, expressed in terms of molar ratios to one of the major components glucosamine), were essentially the same and were indicative of the presence of glycoproteins and mucoproteins. Glycopeptides were prepared on a large scale from FMA-membranes by pronase digestion, then were fractionated into three major fractions, I, II, and III. The distribution of the total carbohydrates found in the pronase digest was roughly 60, 30, and 10% in I, II, and III, respectively. I was a mixture of glycopeptides of relatively low molecular weight, retarded by a Sephadex G-50 column. The carbohydrate moieties were composed mainly of fucose, galactose, mannose, glucosamine, and sialic acid, and appeared to be linked to asparagine through an N-glycosidic (aspartylglycosylamine) linkage. II was a mixture of high molecular weight glycopeptides, excluded from a Sephadex G-50 column. Its carbohydrate moieties were composed mainly of galactose, glucosamine, galactosamine, and sialic acid, and were probably linked to threonine and serine through an O-glycosidic linkage. II was capable of binding to a lectin from Ricinus communis which is galactose or N-acetylgalactosamine specific. III was a mucopolysaccharide identified as heparan sulfate on the basis of its chemical composition, the presence of N-sulfate, electrophoresis on cellulose acetate and its resistance to chondroitinases [EC 4.2.2.4]. Glycopeptides similarly prepared from Zn-membranes gave two fractions corresponding to I and II plus III. From the latter, II and III were identified by electrophoresis on cellulose acetate as identical with II and III from FMA-membranes, respectively.