||This study concentrated on the effect of CYP3A5 polymorphism on cyclosporine (CsA) pharmacokinetics in Thai renal allograft recipients. A prospective descriptive study design was used. Thirty-four renal transplant outpatients who were on microemulsion CsA (Neoral®) and have had stable renal allograft function for at least 3 months were recruited. CsA dose and general demographic data of the patients were recorded. The CsA concentrations at C0 and C2 were determined in whole blood using the chemiluminescent microparticle immunoassay (CMIA). CYP3A5 genotyping was determined by real-time PCR technique. The results obtained indicated that CYP3A5 polymorphism was correlated with CsA dosage requirement in Thai renal transplant patients. The weight-adjusted dose was significantly higher in the CYP3A5*1/*1 group as compare to CYP3A5*1/*3 and CYP3A5*3/*3 group (2.66±0.49 vs 2.07±0.53 mg/kg/day, p=0.028) while the dose-adjusted C0 and C2 showed tendency to be lower in the CYP3A5*1/*1 group as compare to the other group.