The aim of this work was to evaluate in vitro suceptibility of twenty strains of Serpulina hyodysenteriae to five antimicrobial agents, two of them widely used in field outbreaks of Swine Dysentery in Argentina. Field strains of Serpulina hyodysenteriae were obteined from Swine Dysentery cases. Five drugs were used: Carbadox, Tiamulin, Lincomycin, Tylosin, Sedecamycin. Minimal Inhibitory Concentration Test was determined by the agar block dilution test. The results obtained indicate that Carbadox was the most effective antimicrobial agent in vitro against Serpulina hyodysenteriae, followed by Tiamulin. Tylosin, Lincomycin and Sedecamycin had poor efficacy in vitro against Serpulina hyodysenteriae isolates.Facultad de Ciencias Veterinarias