Exposure of primary turkey kidney cell cultures to 100 micrograms/ml wheat germ agglutinin (WGA), a lectin that binds N-acetylglucosamine (NAcGl), significantly inhibited invasion of the cells by Eimeria meleagrimitis sporozoites. However, neither succinyl-WGA, a lectin that retains an affinity for NAcGl but does not bind sialic acid, nor pokeweed mitogen, another lectin that binds NAcGl, similarly inhibited invasion. Collectively, the data suggested that the inhibition of invasion may be caused primarily by binding of WGA to anionic moieties on the host cell surface and not to specific binding to NAcGl. Exposure of cells to concanavalin A, phytohemagglutinin, or Ricinus communis lectin, as well as with pokeweed mitogen, failed to inhibit invasion by the sporozoites. Ultraviolet microscopy, using fluorescein-conjugated lectins, showed that the lectins had bound to the surface of the cultured cells. No binding of NAcGl or lectins to the surfaces of the sporozoites was demonstrated by either the clumping of the parasites in different lectin concentrations or the use of fluorescein-conjugated lectins. However, exposure of E. meleagrimitis sporozoites to NAcGl increased invasion of untreated cells by 50%.