Cyclosporine A, with individual varieties in absorptive properties, needs a separate dose adjustment for each patient.In a prospective design, from October 2004 to June 2005, 64 renal transplanted children, who had renal transplantation at least 3 months before, at Namazee Hospital, were enrolled in our study. Immunosuppressive regimen consisted of Cyclosporine and prednisolone plus Cellcept or Immuran. Data regarding GFR, serum creatinine, electrolytes, lipids and C₀ and C₂ levels was collected at beginning, in one-month, and five-month intervals. Cyclosporine was adjusted to 100-250 ng/ml based on C₀ level. Patients were divided into two C₀ (<100 and >=100 ng/ml) and two C₂ (<800 and >=800 ng/ ml) subgroups. Mean creatinine at the end of study was statistically similar to values at beginning (1.27+/-1.08 v/s. 1.24 +/- 0.63 mg/dl). The same was true for GFR (84.91 +/- 27.03 v/s. 78.22 +/- 27.08 ml/min), C₀ (127.56 +/- 51.15 v/s. 128.89 +/- 75.38 ng/ml) and C₂ levels (569.96+/-195.82 v/s. 529.22+/-276.71 ng/ml). C₀ level was found to be correlated to C_2- (r=0.74, P=0.01). In addition, C₂ level was correlated to cyclosporine dosage (r=0.52, P=0.01). However, C₀ level was negatively correlated to creatinine (r=-0.07, P<0.05). The coefficient of variation of the three samples of each patient was 10.89% for C₀, 8.94% for C₂ while the drug dosage kept constant. Similar creatinine levels, drug dosage, and complications of C₀ and C₂ subgroups may be due to dependence of renal function to several factors other than cyclosporine dosage. Regarding coefficient of variation, C₂ was more accurate and reliable than C₀ level. As there was no significant difference in mean C₀ and C₂ levels, and renal function at beginning and the end of the study, there seems to be no need to check C₂ levels after renal transplantation.