Successful kidney transplantation has gradually improved over the years; much of the improvement has resulted from the use of CsA. However, adequate and tolerable immunosuppression is difficult to achieve with CsA, and rejection episodes are still frequent. CsA is nephrotoxic, with drug toxicity often masking rejection episodes. Other immunosuppressant therapies can result in a range of complications, including metabolic disturbances, adrenocortical insufficiency, and increased risk for infections. Therefore, more effective drugs with less toxicity are needed to prevent acute rejection, especially in the pediatric population where the overall graft survival rate remains significantly lower when compared with that of adult transplant recipients. SRL is an immunosuppressive agent being developed for the prophylaxis of acute renal allograft rejection. SRL has a unique mechanism of action. It inhibits T and B cell activity. In Phase I and II trials in adults, SRL was generally well tolerated and exhibited no apparent nephrotoxic properties, and significantly lower rates of rejection were seen with SRL when compared to placebo.