Twenty adult kidney transplanted patients treated with Prograf® twice daily or Advagraf® once daily will be included in the study. Eligible patients may be included in a stable posttransplant phase (no Tac dose adjustments or acute rejection episodes the preceding 2 weeks). A 3-hour hyperglycaemic clamp will be performed while patients are treated with their standard Tac formulation and repeated 4-6 weeks after switching to the alternative Tac formulation. The clamp investigation will be done after administration of the morning dose of Tac. Samples for measurement of Tac whole blood concentrations will be drawn for all patients up to 24 hours after morning Tac dosing. It is not mandatory for all patients to perform full 24 hour pharmacokinetic investigations.