 i. Inclusion criteria Adult patients 18 years, non-infected afebrile, lack of constitutional symptoms and no leukocytosis, on a stable PD regimen at least one month are eligible for participation. Both patients with and without residual renal function will be studied. Non-anuric patients concurrently receiving medications with the potential to inhibit active tubular secretion will be allowed to enter the study after a 2-week washout period. These medications include H2-antagonists, trimethoprim, or probenecid. The patient and their physician at the Hortense and Louis Rubin Dialysis Center will contacted if any medication needs to be discontinued. 