 The significance of these studies is based on several factors: 1 Calcineurin inhibitor-induced renal insufficiency is a major source of morbidity and mortality among LTx recipients; 2 Once it is established, there is no effective treatment for calcineurin inhibitor-induced renal insufficiency; and 3 If the results of this study support our hypothesis, we will be able to embark upon a full scale, randomized trial of long-term oral L-arginine supplement using GFR as the end point. Such a study will be able to answer whether a simple amino acid supplement may prevent calcineurin inhibitor nephrotoxicity, making a fundamental difference in morbidity, mortality and quality of life of our patients, who have undergone a life-changing procedure, namely liver transplantation. 