Even though improved husbandry has reduced the level of porcine pleuropneumonia caused by Apl, this disease is still a significant problem for the swine industry. Current vaccines do not adequately protect against disease. We have characterized 4 mutant strains of A. pleuropneumoniae which could be developed into a live attenuated vaccine for prevention of porcine pleuropneumoniae. These strains would be administered by intranasally. The intranasal route of administration of the vaccine is easy, elicits protective immunity, and does not damage muscular tissue. We were unable to prevent colonization with the wild type serotype 1 strain 4074mm-AP. However, vaccination did reduce the number of wild type bacteria in the lungs compared to unvaccinated pigs. Further modifications are planned to enhance the efficacy of these attenuated live vaccines.