A novel lectin was purified from the coelomic fluid of the sea cucumber Holothuria scabra (HSL), subjected to bacterial challenge. HSL is a monomeric glycoprotein of molecular mass 182 kDa. The lectin is highly thermostable as it retains full activity for 1 h at 80 degrees C. Further, the hemagglutination activity of HSL is unaffected by pH in the range 2-11. Unlike other lectins purified from marine invertebrates, the hemagglutination activity of HSL does not require any divalent metal ions. The affinity profile of HSL was studied by a combination of hemagglutination inhibition and fluorescence spectroscopy. HSL binds to desialylated glycoproteins, Me alpha Gal, T-antigen and T (alpha - ser)-antigen with a distinction between Beta 1-4 and Beta 1-3 linkages. Me alpha -T-antigen was a potent ligand having highest affinity (K sub (a) 8.32 x 10 sup (7) M sup(-1)). Monosaccharide binding is enthalphically driven while disaccharide binding involves both entropic and enthalpic contributions.