Experimental swine dysentery was produced in groups of susceptible pigs by feeding pure cultures of two isolates of T hyodysenteriae. These infected groups of pigs were then used to assess the efficacy of ronidazole medication of the drinking water and of the feed in the treatment and prophylaxis of the experimental disease. Ronidazole was found to be effective in the treatment of swine dysentery and appeared to eliminate the causal agent, T hyodysenteriae, from treated affected pigs when given in the drinking water at 30 and 60 ppm for three days and in the feed at 120 ppm for four days. The inclusion of ronidazole in the feed for 14 days at 30, 60 and 90 ppm was found to suppress the development of the disease but 90 ppm was the only level found to prevent the development of infection.