In commercial pigs barns pigs often have their immune systems stimulated (ISS) as they are expose to all sorts of air born pathegons and other challenging environmental factors. This has negitive impacts on productive growth, nutrient utilization and profitability. This study attempts to find  a way that nutrition can reduce the negitive impacts of immune system stimulation on growth performance. The focus was on important amino acids that are involved with the immune system: methionine, cysteine and tryptophan. ISS was acheived by injecting pigs with a challenger, various indicators of ISS, including body temperature, were monitored to confirm effectiveness of ISS. The research showed that ISS does not influence nutrient digestibility, but reduces the pig’s growth performance potential. All three of the amino acids had increased dietary requirements when the immune system was stimulated. This research can allow for recommendations about adjusting intake of the three key amino acids to optimize the pig’s response to poor environmental factors that increase the chance of disease.