SUMMARY Enzymatic analysis of the venous effluent of ischemically injured kidney failed to predict accurately the ability of an ischemically injured kidney to support life. Postoperative serum assay of lactic dehydrogenase (LDH) is of value in the assessment of the functional status of the kidney and correlates with response of the rejection episode to immunosuppression. However, by itself it cannot be a sole guide to withholding of therapy. Successful treatment is associated with a decline in LDH level, and failure to return to base line serves as a guide to irreversibility of the rejection reaction Assessment of the functional status of the renal allograft before and after transplantation poses diagnostic problems with significant therapeutic implications. Disturbances in metabolism and cellular integrity are to be expected in even the most ideal circumstances. Numerous factors or a combination of factors frequently result in significant functional impairment of the transplanted kidney. To determine etiology as well as the extent of this injury, invasive studies such as angiograms, biopsies, and scans are performed. These studies are frequently equivocal, and therapy relies on the experience of the transplant team. Reliable parameters upon which judgment of allograft vaibility can be based are not available. Since hypoxia is associated with loss of cellular membrane integrity, liberation of measurable enzyme content indicative of the degree of injury should occur. The purpose of this study is to assess the reliability both experimentally and clinically of serial enzyme analysis in the assessment of organ viability before and after transplantation