Non-compliance in solid transplantation recipients is a major factor in acute graft rejection, which influences patient survival. Nowadays, tacrolimus is one of the most widely used immunosuppressant agents together with cyclosporine following kidney and liver transplantation with a standardized twice-daily dosing regimen. To improve the patients'compliance to the prescribed immunosuppressive therapy, FK506E (MR4), a modified release (MR) oral dosage form of tacrolimus has been developed for a once-daily dosing regimen. This report reviews the most recent results of clinical trials with MR tacrolimus after kidney and liver transplantation.