Specific glycosylation inhibitors were used to show that N-glycans, and not O-glycans or glycolipids, constitute the major class of receptors on 3T3 cells for polyoma virus. Sialic acid (SA)-specific lectins were used in attempts to confirm the expected SA linkage on N-linked glycans. A lectin specific for alpha2,6 linked SA, a non-receptor type, was slightly more effective in blocking infection than a lectin specific for alpha2,3 linked SA which corresponds to the known receptor specificity. Possible explanations are suggested for this unexpected result.