Minimal infectious doses have been determined for intranasal and Salmonella contaminated environmental models of acute Salmonella infection. Trials 1 and 2 were conducted in which Salmonella enterica subspecies enterica serovar Typhimurium were intranasally inoculated at levels of 1 X 101 , 1 X 103 , and 1 X 105 (trial 1) or 1 X 103 , 1 X 105 and 1 X 107 (trial 2) colony forming units (CFU) per animal (5 animals per principle group). Trials 3 and 4 were conducted in which S. Typhimurium were used to contaminate holding pens to levels of 1 X 101 , 1 X 103 , and 1 X 105 (trial 3) or 1 X 103 , 1 X 105 and 1 X 107 (trial 4) CFU per gram of feces (5 animals per principle group). Pigs were necropsied 3 hours following intranasal inoculation or introduction into a Salmonella contaminated environment. Blood, tonsil, mandibular lymph node, thymus, lung, liver, spleen, ileocecal lymph node, kidney, muscle, ileum, colon contents, and cecum contents were collected for Salmonella isolation and qualitatively recorded for the presence of Salmonella. These results indicate minimal levels in which Salmonella must be controlled during transportation and lairage in order to reduce acute Salmonella infection immediately prior to slaughter.