Several in vitro and animal studies demonstrate cysteine supplementation increases glutathione concentrations in the blood, liver, and intestines. Cysteine supplementation to premature neonatal erythrocytes in cell cultures have demonstrated increased glutathione concentrations compared to non-cysteine supplemented controls. Malloy et. al. have shown cysteine-HCl supplemented TPN-fed beagle pups have higher concentrations of plasma cysteine and hepatic glutathione than unsupplemented TPN-fed pups. Similarly, Pollack et. al. have demonstrated intestinal glutathione concentrations significantly increase in premature newborn rabbits administered cysteine-HCl supplementation compared to non-supplemented controls. Moreover, the colonic glutathione concentrations were found to be similar to those of maternally reared, term newborn rabbits.