A study was undertaken to answer questions about the epidemiology of Salmonella in pig production. Does the Salmonella excretion from a group of pigs (on the same farm) remain constant during time or is there variations ? Where, and how many samples do we have to take to follow these variations, if they exist? Are the techniques to analyse samples (bacteriological and serological) practicable ? How is the relationship between serological and bacteriological methods?