By affinity chromatography on peanut agglutinin-agarose, receptors for peanut agglutinin were isolated from three lines of human malignant cells labeled with [3H]-galactose. The cell lines examined were a Burkitt lymphoma line Daudi, a lung squamous carcinoma QG-56 and a gastric signet ring carcinoma KATO-III. The isolated receptors from the three sources had similar properties and behaved as glycoproteins with apparent molecular weights of 160,000 to 280,000 upon sodium dodecyl sulfate gel electrophoresis. However, they showed molecular weights of only around 70,000 upon gel filtration, suggesting that they contained large amounts of carbohydrates. Pronase digestion depolymerized the glycoproteins, though significant amounts of the products were large enough to be excluded from a column of Sephadex G-50. The large molecular weight products were not detected when the receptors were treated with mild alkali and NaBH4 prior to pronase digestion. Major components of the radioactive oligosaccharides and glycopeptides released in the latter case had molecular weights in the range from 3,500 to less than 1,000. These results indicate that the glycoprotein receptors had clusters of oligosaccharide chains of small and medium sizes.