Mycophenolate acid (MPA) has been developed and approved in combination with cyclosporine and has been used in kidney transplantation for more than a decade. At present, combination of tacrolimus and mycophenolate acid tends to be considered as the standard of care for maintenance immunosuppression in kidney transplantation. Mainly due to a different effect on the entero-hepatic recycling pathway, cyclosporine and tacrolimus differently interfere with MPA clearance. When used with tacrolimus, MPA dosage has thus to be adjusted and cannot be extrapolated from what is recommended for a cyclosporine-based treatment. However, there is currently no clear guideline for MPA dosing when this drug is used in combination with tacrolimus. This is potentially detrimental for patients since under-or overexposure of MPA has been clinically linked to the outcome of transplantation.