We determined the cross-reactivity of a monoclonal antibody against the Macrobrachium rosenbergii lectin with proteins in the hemolymph from Procambarus clarkii (Pc), Procambarus americanus (Pa), Litopenaeus setiferus (Ls), and Pseudothelphusa americana (Psa). Crustaceans' hemolymph agglutinated erythrocytes from rat, mouse, guinea pig, and rabbit. Decapods' hemolymph hemagglutinating activity was inhibited by N-acetylated carbohydrates as well as by antibodies. Western blot assays indicated that the antibodies recognized two main proteins of 97.5 and 80.9 kDa in all hemolymphs studied; moreover, ELISA assays indicated that, in PSa, 7.2% of total proteins showed crossreactivity with antibodies in Pa, Pc, and Lc hemolymphs represented 4.2, 3.1%, and 2.5%, respectively. Our results suggested that antibodies recognize the lectin active site in the crustacean species tested; we propose the use of antibodies as an immunological marker for lectin identification and quantification among crustaceans.