The aggregation of single-cell suspensions of normal and four ricin-resistant cell lines of baby hamster kidney (BHK) cells by several lectins has been studied by particle counting. Normal BHK cells were aggregated by concanavalin A, Ricinus communis agglutinin and ricin, Abrus precatorius agglutinin, wheat germ agglutinin, and Erythrina cristagalli and Erythrina corallodendron agglutinins. Neuraminidase treatment increased 4–13 fold the aggregation of BHK cells by the latter two lectins, as reported earlier for ricin (see ref. 13). After long-term culture of normal BHK cells with swainsonine, an inhibitor of complex N-glycan assembly, the aggregation of cells by each lectin except concanavalin A was much decreased or totally abolished. The lectin-induced aggregation of ricin-resistant cell lines Ric R 14, 15, 19, and 21 was very similar to swainsonine treated BHK cells. Aggregation of Ric R 15, 19, and 21 cells by Erythrina lectins was increased markedly by neuraminidase treatment of the cells. A smaller effect was obtained with Ric 14 cells. The data reported are consistent with similar hybrid N-glycans being present in swainsonine-treated BHK cells and the ricin-resistant cells. The hybrid structures bind lectins of Ricinus, Abrus, and Erythrina species after desialyation.