We examined the IgE-binding reaction and the histamine-releasing response of basophils to a panel of 12 lectins: concanavalin A (Con A), Lens culinaris hemagglutinin (LcH), Pisum sativum agglutinin (PSA), wheat germ agglutinin (WGA), soybean agglutinin (SBA), Bauhinia purpurea agglutinin (BPA), peanut agglutinin (PNA), Ricinus communis agglutinin I (RCA-I), Lotus tetragonolobus agglutinin (Lotus A), Ulex europeus agglutinin I (UEA-I), phytohemagglutinin E (PHA-E) and phytohemagglutinin L (PHA-L). IgE from allergic patients bound with high affinity to Con A, LcH, PSA, RCA-I and PHA-E, and with lower affinity to WGA, BPA, Lotus A and UEA-I, but they did not bind to SBA, PNA or PHA-L. There was no apparent individual difference in the reactivity of IgE to these lectins between 10 IgE preparations from allergic patients. The binding to these lectins, except Lotus A and UEA-I, were competitively inhibited by the lectin-specific sugars or glycopeptide. Upon stimulation by Con A, LcH, PSA, WGA, RCA-1 and PHA-E, leukocytes from allergic patients showed a significant release of histamine, but cells from IgE-deficient subjects did not respond to these lectins. The histamine-releasing responses by these lectins were also inhibited by specific sugars or glycopeptides.