A novel lectin was isolated from hemolymph of American horseshoe crab Limulus polyphemus by using human glycophorin A N affinity chromatography and Sephacryl S-300 gel filtration. The lectin's molecular weight was approximately 1700 kDa; being composed of 24 identical subunits with molecular weights of 70 kDa. The hemagglutinating activity of the lectin against human erythrocytes was strongly inhibited by human glycophorin A N and weakly inhibited by N-acetylhexosamines, although not inhibited by neutral sugars, or hexosamines. This lectin required no Ca 2 + for hemagglutinating human, rabbit and equine erythrocytes, respectively.