Four trials were made to study the possibility of fattening pigs free from Salmonella under field conditions. One pig-sty on a Salmonella-contaminated farm was used in these studies. Previous studies had shown that Salmonella-free fattening pigs could be produced under experimental conditions. A number of hygienic measures were adopted on the farm, such as the purchase of Salmonella-free piglets, the use of correctly pelleted feed, thorough cleaning and disinfecting of the pig-sty, and the prevention of all infections originating from the environment. Notwithstanding all these measures, completely Salmonella-free pigs could not be obtained. In three out of four experiments, even a mass infection with Salmonella even became apparent among the pigs. During the experiments a number of possible routes of infection were detected. The presence of these possible routes of infection was due to the fact that the measures referred to were not carried out accurately. This suggests that it will be very difficult to satisfy the requirements of strict hygiene under field conditions. Further experimental studies will have to show whether this is usually the case. During the third and fourth trial, studies were not confined to the farm, but also extended to the period of slaughter. From these investigations it became apparent that transport to as well as the period of waiting in the slaughter-house also provide several opportunities for contamination of the pigs, in spite of extensive cleaning and disinfection of both cattle-truck and lairages.