Allograft rejection can be classified as humoral or cellular mechanisms. Accurate diagnosis of acute rejection remains a formidable challenge in renal transplantation. The need to avoid unnecessary immunosuppressive therapy to treat this complication has led to a continued search for improved diagnostic methods to evaluate and identify postoperative episodes. Here we evaluated the use of [(99m)Tc]OKT3 scintigraphy to diagnose acute rejection in renal transplants. Among 22 patients undergoing renal transplant, we observed an increased [(99m)Tc]OKT3 kidney uptake with the passage of time in patients with rejecting allografts. These findings agreed with those of biopsies. We suggest the [(99m)Tc]OKT3 scans may be useful for the monitoring of renal transplants to detect acute rejection.