Murine interleukin-2-dependent T-lymphocytes (CT6) were treated with tunicamycin, an inhibitor of both glycoprotein and ganglioside synthesis, to study the involvement of glycosylation in the IL-2 proliferative response. Tunicamycin inhibited proliferation in a dose-dependent manner at concentrations which did not inhibit protein synthesis (10-50 ng/ml). Swainsonine, a glycoprotein processing inhibitor, had no effect on proliferation. Inhibition of proliferation by tunicamycin was accompanied by an inhibition of binding of 125I-IL-2 to its high-affinity receptor. Scatchard analysis showed that receptor number was decreased by tunicamycin treatment. On the other hand, tunicamycin did not affect either the binding of the monoclonal antibody 7D4, specific for the 55 kDa low-affinity protein subunit of the IL-2 receptor, or the recycling of the IL-2 receptor. To determine the specific effects of tunicamycin on the biosynthesis of particular CT6 glycoconjugates, cells were radiolabeled with 3H-glucosamine and incorporation into ganglioside, neutral glycolipid and glycoprotein fractions was measured. Low doses of tunicamycin inhibited ganglioside synthesis and glycoprotein glycosylation to the same extent, whereas no effect on neutral glycolipid synthesis was observed. These results suggest that glycosylation of glycoprotein and/or gangliosides might play an important role in the formation of a functional high-affinity IL-2 receptor complex in CT6 cells.