A strain of Haemophilus pleuropneumoniae was isolated from a pig with pleuropneumonia from a herd where this condition was frequent. A formalin inactivated culture of this isolate was used as antigen in two vaccine preparations: A and B. Vaccine A had peanut oil + arlacel 80 + tween 80 as adjuvant and vaccine B had aluminum hydroxide gel as adjuvant. Twenty pigs were vaccinated twice with vaccine A and 19 with vaccine B. Twenty additional pigs were not vaccinated. All pigs were transferred to the herd. Eleven pigs in the nonvaccinated group developed pneumonia and seven of these died within eight days after exposure. None of the vaccinated pigs had signs of pneumonia. It is concluded that the vaccines prevented the acute form of pleuropneumonia due to H. pleuropneumoniae.