<prompt> Hyperacute rejection occurs within:?12 hours2 weeks1 month3 months  <response>: Ans. a 12 hoursRef: Robbins 9th ed p 233Hyperacute rejection occurs when preformed antidonor antibodies are present in the circulation of the recipient. This form of rejection occurs within minutes or hours after transplantation. A hyperacutely rejecting kidney rapidly becomes cyanotic, mottled, and flaccid, and may excrete a mere few drops of bloody urine. Immunoglobulin and complement are deposited in the vessel wall, causing endothelial injury and fibrin-platelet thrombi. 