Pork is a major cause of foodborne salmonellosis. Consequently, effective measures that could reduce the prevalence of Salmonella at the farm are of interest. In the present study, three field trials were performed to evaluate the effect of strategic administration of organic acids, at concentrations estimated by economic criteria, on the Salmonella prevalence in finishing pigs. Pigs received either a mixture of acids (lactic, formic, propionic, and acetic) added to their drinking water at a concentration of 0.035% (trial A), or a basal diet containing 0.5% potassium-diformate, KH(COOH)₂, (trials B and C), during the last 6-7 weeks of the finishing period. Fecal Salmonella shedding and seroprevalence were monitored in the animals at four time points during the study. Mesenteric lymph nodes and cecal contents were collected from a subset of animals at the slaughterhouse and cultured for Salmonella. At the end of the finishing period in all three trials, the percentage of seropositive pigs was higher in the control group than in the experimental group, regardless of which cutoff value was used in the enzyme-linked immunosorbent assay (ELISA) assay. The frequency of fecal shedding was lower also in the treated pig groups from the trials A and B at the end of the finishing period. The results from the samples collected at the slaughterhouse did not yield differences between groups in trials A and B. However, Salmonella isolation was less frequent in the mesenteric lymph nodes from the experimental pigs in trial C. The seroprevalence reductions, together with some promising results in the reduction of shedding, support the idea that this intervention is a useful strategy to reduce Salmonella prevalence at the farm.