The rapid understanding of the cellular and molecular basis of organ function and disease processes will be translated in the next millennium into new therapeutic approaches to a wide range of clinical disorders, including acute and chronic renal failure. Central to these new therapies are the developing fields of gene therapy, cell therapy, and tissue engineering. These new technologies are based on the ability to expand stem or progenitor cells in tissue culture to perform differentiated tasks and to introduce these cells into the patient either in extracorporeal circuits or as implantable constructs. Cell therapy devices are currently being developed to replace the filtrative, metabolic, and endocrinologic functions of the kidney lost in both acute and chronic renal failure. This article summarizes the current state of device development for a renal tubule assist device, a bioartificial hemofilter, and a regulatable erythropoietin cell therapy device. These individual devices have the promise to be combined to produce a wearable or implantable bioartificial kidney for full renal replacement therapy. These new approaches may result in therapeutic modalities that significantly diminish the morbidity and mortality in patients with acute renal failure or end-stage renal disease.