Immuno recognition (and therefore contribution to defense mechanisms against infectious diseases) has long been one proposed role of lectins in crustaceans and other invertebrates. Studies in this and other laboratories have shown the inducibility of lectins in response to "antigen", and evidence of a "memory" component to the response with respect to the levels of lectins attained upon secondary induction of lectins by antigen. The present study reports the characterization of two lectins isolated and purified from the hemolymph of the brown shrimp, P. aztecus. One lectin, designated as PAL-I, was purified by affinity chromatography using a fetuin-agarose gel. The purified lectin showed homogeneity by SDS-PAGE, and had a subunit molecular weight of 34,000 daltons. It produced a single peak on gel filtration by HPLC, showing a native molecular weight of approximately 200,000 daltons. Its isoelectric point was 5.25 as determined by isoelectric focusing (IEF). It was a glycoprotein as indicated by DIG glycan staining and the DIG glycan differentiation test strongly suggested that it was an N-linked glycoprotein. The lectin agglutinated erythrocytes from a number of species. In agglutination inhibition studies using rabbit crythrocytes, its agglutination activity was specifically inhibited by N-acetyl group on taining sugars such as N-acetylneuraminic acid, colominic acid (a homopolymer of NANA), N-acetylneuraminic-lactose, N-cetyl muramic acid, N-acetylglucosamine and N-acetylgalactosamine. It was a calcium dependent lectin as shown by agglutination inhibition in the presence of EDTA and recovery of agglutination activity upon subsequent addition of calcium. The second lectin, designated as PAL-II was purified by affinity chromatography on bovine submaxillary mucin (BSM)-poly galactose gel, following by gel filtration by HPLC. The lectin showed homogeneity on SDS-YAGE with a subunit molecular weight 14,400 daltons. Its native molecular weight was 77,000 dalton as indicated by HPLC gel filtration. It was not glycosylated. Agglutination inhibition (using rabbit erythrocytes) was specifically inhibited by lactose. It also was a calcium dependent lectin.