Seventy-two conventionally raised pigs were challenge exposed intranasally when approximately 3.5 weeks old with yolk-grown Bordetella bronchiseptica. Twenty-four pigs acted as noninfected, nonmedicated controls. Feed containing sulfamethazine or sulfathiazole (110 mg/kg of feed) was initiated in 2 groups of 24 infected pigs each 3 days after challenge exposure and was fed continuously for 56 days. Twenty-four infected pigs were given nonmedicated feed. Challenge exposure with the B bronchiseptica resulted in nasal bordetellosis characterized by isolations of the test organism from nasal cavities of infected control pigs at greater than 90% frequency through 28 days and from at least 50% of the pigs through 56 days. Moderate turbinate atrophy developed with a 48% increase in mean turbinate space in infected control pigs at necropsy. Performance was not affected by the infection which was confined to the nasal cavity. The B bronchiseptica isolation rate decreased faster (P less than 0.01) in the sulfamethazine group than in the sulfathiazole group. By day 42, sulfamethazine-medicated pigs were negative for B bronchiseptica in nasal swab samples; whereas 8% to 17% of sulfathiazole-medicated pigs were positive from days 42 to 56. Turbinate spacing measurements averaged 11% less in the sulfamethazine group than in the sulfathiazole group.