An important part of the salmonella surveillance programme in Danish slaughter pig herds (Mousing et al. 1997) is to reduce the occurrence of salmonella in herds with a moderate to high proportion of subclinically infected pigs. This includes advisory visits in infected herds where veterinarians and consultants inspect the herd and define changes in management in order to reduce the infection level. A good understanding of the relationship between risk factors and occurrence of salmonella is essential to control infection and to avoid spread of salmonella among and within herds. In study 1, management and factors related to feeding in randomly selected herds and herds with a high sero-prevalence were compared in order to determine factors that could affect the risk of salmonella infection. Study 2 was an epidemiological analysis of the association between serological results and management factors in herds selected from two slaughterhouse-cooperations.