In a study of the saliva-induced aggregation of Streptococcus mutans, it has been found that saliva pretreated with wheat germ agglutinin (WGA), a lectin with a high specificity for binding to N-acetylglucosamine (GlcNAc), did not induce the aggregation of S. mutans strains AHT, IB, and V-100. GlcNAc blocked the effect of WGA and restored aggregating activity to some WGA-pretreated saliva supernatants. The solution obtained by dissolving the precipitate from saliva treated with 256 μg/ml WGA in buffer containing 200 mM GlcNAc and 1 mM CaCl2, also aggregated S. mutans. The results suggest that WGA reversibly binds to a salivary aggregating factor containing GlcNAc