2. To determine the influence of CYP3A5 polymorphism on clinical outcome of kidney transplantation recipients Review article Kidney transplantation is the most appropriated treatment in end stage renal failure patients in order to improve quality of life. National health security office of Thailand estimates the cost of kidney transplantation around 250,000 to 400,000 baht per patient. However, patients have to take immunosuppressive drugs such as cyclosporine, tacrolimus, azathioprine, mycophenolate, prednisolone etc. to prevent graft rejection. Tacrolimus is a common immunosuppressive drug used worldwide. However, tacrolimus has narrow therapeutic level and needs regularly therapeutic monitor because of inter-individual variation in dosage regimen. Achieving and maintaining target concentration of tacrolimus are related to tacrolimus toxicity and graft rejection. Not only age, body weight and drug interaction but also genetic factor in metabolic pathway of tacrolimus plays an important role in tacrolimus blood level.