Hemolin, a plasma protein from lepidopteran insects, is composed of four immunoglobulin domains. Its synthesis is induced by microbial challenge. We investigated the biological functions of hemolin inManduca was found to bind to the surface of bacteria and yeast, and caused these micro-organisms to aggregate. Hemolin was demonstrated to bind to lipopolysaccharide (LPS) from Gram-negativebacteriaand to lipoteichoic acid fromGram-positive bacteria.