It is customary for patients undergoing kidney transplantation to receive their first dose of cyclosporin either just before or during the transplant operation. This ensures the early establishment of good levels of immunosuppression but might depress early graft function and contribute towards the development of acute tubular necrosis. In a controlled clinical trial, we have studied the effects of withholding cyclosporin for 12 h in patients undergoing cadaveric renal transplantation. Consecutive adult recipients of a cadaveric renal transplant were randomised to receive their first dose of cyclosporin (10 mg/kg p.o.) 6 h prior to transplant surgery or 12 h afterwards. All patients received azathioprine (1.5 mg/kg i.v.) and methylprednisolone (0.5 g i.v.) in addition during surgery. From the 2nd day onwards both groups were treated with an identical triple immunosuppressive regimen. The 27 patients who received their first dose of cyclosporin post-operatively had significantly better immediate and subsequent function than did the 26 patients who received their cyclosporin at the time of surgery. The delayed dosing was associated with improved graft survival and no increase in the frequency of rejection episodes. This regimen is recommended for all patients receiving triple therapy.