The aim of this study was to evaluate the feasibility and in vitro activity of ligand-conjugates based on the use of poly(methyl vinyl ether-co-maleic anhydride) (PVM/MA or Gantrez AN). Fluorescently labelled PVM/MA nanoparticles were prepared by desolvation and cross-linkage with 1,3-diaminopropane (DP). Conjugates were obtained by incubation between the carriers and Sambucus nigra agglutinin (SNA) for 1 h in an aqueous medium. The lectin binding to the surface of nanoparticles was increased by both increasing the bulk ligand concentration and decreasing the amount of cross-linker. However, a concentration of about 0.3-0.4 mg DP per mg polymer was necessary to obtain maximum agglutination activity. Under optimal conditions, the amount of fixed ligand was 46 microg/mg nanoparticle (binding efficiency of 86%); although the activity of SNA conjugates was 13.3 microg/mg particle. The activity of nanoparticles, measured by the association to Caco-2 monolayers, was higher when SNA was covalently bound onto their surface. The lectin-conjugate interaction was 6-fold higher than conventional nanoparticles. Moreover, energy-dependent mechanisms were only observed in SNA-PVM/MA particles. Finally, the decrease in association in the presence of lactose demonstrates that both SNA- and SNA-conjugate-binding was due to a true lectin-sugar interaction.