 Our hypothesis is that L-arginine will promote the release of NO in the renal vascular bed, increasing renal blood flow and glomerular filtration rate AIM 1. We believe it is critical that we test this in patients early after LTx before irreversible vascular and glomerular damage is established. Once this proof of concept is attained, we would like to link the observation with plasma L-arginine concentration and urinary c-GMP excretion AIM 2. Based on extensive experience at Mayo Clinic of using oral L-arginine, we expect to demonstrate no clinically significant adverse events with L-arginine AIM 3. The data from the open label maintenance phase AIM 4 will help gauge whether the short term benefit shown in AIM 1 is sustainable for a longer time frame. 