The binding of 13 different lectins to gp120 partially purified from two HIV-1 isolates and one HIV-2 isolate was studied by in situ staining on electrophoretically separated and electroblotted HIV antigens. The lectins concanavalin A, wheat germ agglutinin, Lens culinaris agglutinin, Vicia faba agglutinin, Pisum sativum agglutinin and phytohaem(erythro)agglutinin bound to gp120 of all three isolates. The carbohydrate of gp120 recognized by lectins was thus arranged in at least four types of glycans: a high mannose type glycan, a bisected hybrid or complex type glycan, a biantennary fucosylated complex type glycan and a triantennary bisected complex type glycan. Only lectins which bound at least one of the four types of glycans were capable of inhibiting fusion of HIV-infected cells with CD4 cells by a carbohydrate-specific interaction with the HIV-infected cells. Thus, several different glycan structures may be implicated in CD4-gp120 binding.