Nanoparticles with an average size of similar to 100 nm were obtained by ionic gelation of chitosan (M6.5 x 10(3) and 60 x 10(3) Da) in the presence of tripolyphosphate. Dispersions of the nanoparticles showed high antimicrobial activity against pathogenic organisms such asC. michiganensisstrain 101 bacteria andF. graminearumandA. solanifungi.