This study will start with a retrospective data analysis. The investigators will use the electronic databases of National Taiwan University Hospital to identify patients who underwent liver transplantation, received tacrolimus and were still followed up at the outpatient clinic. Inclusion and exclusion criteria will be applied to screen appropriate participants, and find their donors. And analyze the effect of genetic polymorphism (ABCB1、CYP3A4、CYP3A5、POR) of donors, including other factors of recipients, on the dose normalized trough concentration of tacrolimus.