A retrospective survey of 165 United States renal transplant units identified 48 patients who had discontinued all immunosuppressive therapy (IT). Sixteen had received cadaveric and 32 had received living-related grafts. The interval from transplantation to cessation of medication was similar in both groups and did not correlate with the outcome. Of 16 cadaveric grafts, 9 failed ("delta" serum creatinine concentration of greater than or equal to 5 mg/dl) within a mean of 59 days; 3 patients maintained stable renal function for 244, 395, and 425 days, respectively. Of the 32 related grafts, 12 failed within a mean of 234 days. Of the 20 related grafts that did not fail, 5 had stable function for greater than or equal to 1 year and 6 for greater than or equal to 3 years after cessation of IT. Our data demonstrate that at no point after transplantation is it prudent to stop all IT barring serious drug toxicity. Also, in patients who stop IT surreptitiously and in whom renal function remains normal, reinstitution of therapy is indicated within 1 year and is advisable as long as 3 years after cessation; those few patients who do well without IT for greater than 3 years may not need further treatment.