An important part of the Danish salmonella program is surveillance of all Danish pig herds with a yearly deliverance of more than 100 slaughter pigs. Herds categorized in infection level 2 or 3 are obliged to take effort to reduce the seroprevalence of slaughter pigs to an acceptable level. It has been shown, that it is possible to remove pigs from infected herds and raise them to the normal age of slaughter without detectable salmonella infection (Dahl and others, 1996). Based on these results, a model for salmonella reduction on herd level was established. The model consisted of a microbiological survey in the herd to locate infected parts of the herd. Based on the microbiological results a plan for reduction of salmonella was described for each individual farm. A typical plan consisted of hygienic measures combined with all in-all out measures on either pen-level or section level, in combination with an attempt to improve colonization resistance by using organic acids in water or feed.