This was a Phase 1 dose escalation study to evaluate the safety, tolerability and pharmacokinetics of 28-day treatment of CP-690,550 in stable renal allograft recipients. In Stage 1, ascending doses of CP-690,550 were to be administered sequentially to 3-4 cohorts of subjects. After Stage 1, one dose level was to be selected for dosing in an expanded cohort in Stage 2.