The growth of mouse lymphoma L-5178Y cells with a high degree of gangliotriaosylceramide expression (high-expressor clone AA12) was inhibited by the addition of a biotinylated mouse immunoglobulin M monoclonal antibody (2D4) directed to gangliotriaosylceramide followed by cross-linking with avidin or a second antibody (anti-mouse immunoglobulin M). This growth inhibition was observed in both serum-containing medium and a chemically defined medium containing transferrin as the only growth factor. Cell growth was not inhibited by the addition of biotinylated antibody 2D4 alone, avidin alone, or the biotinylated derivative of an immunoglobulin M monoclonal anti-N-acetyllactosamine antibody (1B2) cross-linked with avidin. The growth of lymphoma L-5178Y 27AV cells, which do not express gangliotriaosylceramide (non-expressor clone), was not inhibited by either of these monoclonal antibodies or their biotinylated derivatives plus avidin. In the presence of biotinylated antibody 2D4 and avidin, cells of the high-expressor clone (L-5178Y AA12) displayed a capping of gangliotriaosyl antigen. In contrast, the transferrin receptor and the major glycoproteins (concanavalin A receptors) were not capped in the presence of biotinylated antibody 2D4 and avidin but were homogeneously distributed on the cell surface. Cells whose growth was inhibited by the addition of biotinylated antibody 2D4 and avidin showed an inhibition of 125I-transferrin internalization, although binding of 125I-transferrin to the cell surface was similar to that of control cells. These results indicate that the tumor antigen gangliotriaosylceramide is functionally associated with the transferrin receptor and may regulate the process of internalization of transferrin.