Background and Design.- We porformed this experimental study to investigate the ischemic dam¬ages .related to the preservation time during cadav¬eric renal transplantation using simple cold storage (SCS). Priority was given to investigate the changes of the endothelium due to cold ischemic time and the aggregation of the erythrocytes in the capillaries and arterioles; factors that underlie the "no-reflow" phe¬nomenon. Results.- Although aggregation of the erythro¬cytes in the glomerular peritubular capillaries was a frequent finding, there was no agglutination among the erythrocytes and no adhesion of the erythrocytes to the endothelium following perfusion and a 12 hr preservation. When the preservation time was 24 hr or more, agglutination of the erythrocytes and adhe¬sion of the erythrocytes to the capillary endothelium were seen. There was degeneration of the endothe-lial cells at the adhesion regions and the endothelial completeness was impaired when the cold ischemic time was 48 hr or more. Conclusion.- We have concluded that ultrastruc-tural changes due to long cold ischemic time such as agglutination of the erythrocytes, adhesion of the blood elements to the endothelium and impairment of the endothelial completeness can cause microcir-culation damage and dysfunction of the allograft if reperfusion is performed during renal preservation using simple cold storage.