The study aims to test the influence of vaccination with polyvalent vaccine prototypes on the vibriosis resistance of Penaeus monodon. Vaccinated P. monodon post-larvae were challenged with a virulent Vibrio alginolyticus strain 10, 20, and 30 days post-vaccination. Results showed that vaccination significantly enhances the resistance of shrimp to vibriosis. This effect decreased by age of the post-larvae, particularly for the glucan group. (C) 1998 Elsevier Science B.V. All rights reserved.