Guinea pigs in several groups of five each were inoculated by intramuscular injection with 1.0 · 10 9 CFU of recombinant attenuated S. choleraesuis in 0.1 mL of saline. Thirty-six hours after inoculation, FMDV challenge was carried out via intradermal injection of each animal with 0.1 mL of guinea pig infectious dose 50 ID 50 of HKN/2002 in the left rear foot, as was done for virus titration.