Chitin exhibited a bacteriostatic effect on Gram-negative bacteria, E. coli ATCC 25922, V. cholerae, S. disenteriae and B. fragilis. Chitosan exhibited a bacteriostatic effect on all bacteria tested, except S. typhimurium. The oligomers exhibited a bactericidal effect on all bacteria tested. Differences in activity were exhibited between the type and/or molecular weight of the chitinous material and the bacterial species. Chito-oligomers would have advantages as new antimicrobial agents due to their higher activity and since they are also more readily soluble in water than the native polysaccharides. On a commercial basis N-acetyl chitooligosaccharides (NAc-COS) would be preferred since it is prepared directly from chitin without the need for a deacetylation step, while chito-oligosaccharides (COS) must be prepared from chitosan. Both have similar antibacterial activity. Further work is needed to better understand the mode of action of chitin, chitosan and its oligomers as antimicrobial agents.