The Pig Health Control Association launched a health scheme for atrophic rhinitis in 1978. For several years pig herds were monitored by scoring the degree of turbinate damage and by clinical inspections. When laboratory facilities became available for detecting toxigenic Pasteurella multocida, nasal swabs were taken from pigs in Association herds during 1988 and 1989 to determine whether the organism was present. Sows were screened routinely and in the worst affected herds, sucklers and weaners were also swabbed. In 12 of 19 herds with consistently low snout scores toxigenic P multocida were not isolated, and in 15 herds which developed higher snout scores with time toxigenic P multocida were also not found. Eleven herds had never been listed by the Association, either because their snout scores were consistently high or because they had received importations of stock from herds with high snout scores; of six of these herds with the most persistently high snout scores five showed varying degrees of the clinical signs of atrophic rhinitis, but none of the six showed evidence of infection with toxigenic P multocida, and the organism was not found in the other five herds in the group. There seems to be an overlap between the clinical and gross pathological signs of atrophic rhinitis seen in some herds not infected with toxigenic P multocida and the mild and spasmodic signs of atrophic rhinitis seen in some herds which are substantially infected with the organism.