We studied 2 ascites-converted sublines, TA3-Ha and TA3-St, from the murine tumor TA3. Line TA3-St does not grow in allogeneic mouse strains, whereas line TA3-Ha proliferates in all mouse strains. We compared the membrane characteristics of the 2 tumors, using 5 heterophil agglutinins with known carbohydrate specificities. Agglutinins from concanavalin A (Con-A), Phaseolus vulgaris (PHA), Bandeiraea simplicifolia (Bs), Triticum vulgaris (WGA), and Helix pomatia (Hp) were used. TA3-Ha cells were not agglutmated by Con-A, PHA, or Bs, whereas TA3-St cells were. By contrast, Hp agglutinated TA3-Ha but not TA3-St cells. WGA agglutinated both lines. Using 125l-labeled preparations of Con-A or PHA, we found the same number of binding sites for each agglutinin in both lines. A mixture of Con-A + PHA agglutinated living or fixed TA3-Ha cells; we attribute this to Con-A binding sites on PHA, so that lattice formation between the agglutinins can occur and induce agglutination. TA3-Ha cells sensitized with Con-A bound more PHA than untreated cells. The additional PHA could be released by methyl-α-D-mannopyranoside, suggesting that the additional PHA was attached to Con-A molecules which in turn were bound to cell-surface receptors. If PHA was bound directly to cell-surface receptors, it was not released by methyl-α-D-mannopyranoside. The results also show that PHA and Con-A bind to independent cell-surface receptors. Con-A or PHA agglutinated TA3-Ha cells treated with proteases (e.g., trypsin, papain), but not cells treated with neuraminidase. The results suggest differences in carbohydrate-containing macromolecules on the cell surface of the 2 TA3 sublines, some of which are in “crypts” on the surface of the immunoresistant TA3-Ha cells.