Chronic renal disease remains the leading cause of death in cats and there are still no effective treatment options short of renal transplantation. Stem cell therapy using bone marrow derived stem cells has recently been shown to improve renal function in rodent models of renal failure. Stem cells can augment renal function by trans- differentiation into functional renal tubule cells and by local production of growth factors that improve the function of existing tubule cells. In particular, mesenchymal stem cell (MSC) transfer has been shown to promote renal tubule development and suppress development of renal fibrosis. Our lab has developed the techniques necessary to establish mesenchymal cell cultures from cat bone marrow. Therefore, we propose to conduct a pilot study to evaluate the safety and potential efficacy of MSC transfer in 9 cats with naturally-occurring chronic renal disease. Autologous MSC will be generated from autologous bone marrow samples, then expanded in vitro prior to transfer. One MSC sample will be injected into multiple sites on both kidneys of each cat, using ultrasound guidance. Three groups of cats (n= 3 cats per group) will be injected with increasing numbers of MSC. The effects of MSC transfer on renal function, including GFR, will be assessed over a 3 month period. Safety will also be assessed by physical examination, urinalysis and blood work. This study will provide an important proof-of- principle assessment of this promising new approach, which could be readily applied clinically to many cats with chronic renal disease.