Groups of 20 young chickens and turkeys obtained from commercial flocks and placed in pens with pine shavings over concrete floors or from the hatchery and grown on wire, were exposed to avirulent Pasteurella multocida serotype 3,4 cross or virulent P. multocida serotype 3 by drinking water, ocular, subcutaneous, intracutaneous, or palatine cleft routes. A secondary exposure to virulent P. multocida serotype 1 by the palatine cleft route was given 14 days later, except that birds exposed by palatine cleft on the initial exposure were reexposed by drinking water. There was a group of each species for each floor type and each exposure route except palatine cleft, which was performed on litter only. Chickens were more resistant to initial exposure to virulent P. multocida by all routes than turkeys. Chickens showed much less resistance to subsequent exposure to P. multocida serotype 1 than turkeys after exposure to the avirulent organism by the drinking-water route. Avirulent P. multocida administered to chickens or turkeys by subcutaneous or intracutaneous routes and turkeys by drinking water route produced a high degree of resistance to subsequent exposure to P. multocida serotype 1. In a second experiment it was found that wire floors caused many more breast blisters than pine shavings on Pasteurella-exposed or unexposed chickens.