Although the success of renal transplantation is closely linked to the immunosuppression provided by cyclosporin A (CsA), the best way to monitor the blood levels of CsA is still not clear. Trough CsA levels (C(0)) are commonly used, but the 2-h post-dose CsA levels (C(2)) are reported to correlate better with area under the curve. The aim of this study was to evaluate the correlation of C(2) levels with allograft function in adolescent renal transplant recipients in the late post-transplant period (6 months after transplantation) compared with C(0 )levels. The data of 17 adolescent renal transplant recipients (12 males, 5 females) were evaluated retrospectively. The mean age at the time of transplantation was 15.212+/-2.918 years and the mean follow-up period was 53.172+/-34.090 months. C(0) levels correlated with oral CsA and diltiazem doses, while C(2) levels exhibited no correlation. When C(2) levels were classified as 0-400, 401-800, and 801-1200 ng/ml, no statistically significant difference was found between these groups with respect to glomerular filtration rate (P=0.830). Although 82% of the patients had C(2 )beneath the therapeutic level (<800 ng/ml), none had an acute rejection episode. In conclusion, optimum C(2) levels could be different from levels in the adult population. Furthermore, the correlation of C(2) levels with CsA dose seems to be weaker than in the adult population. Thus, further studies are needed to determine a more reliable predictor for CsA dose monitoring and target blood CsA levels in adolescent patients.