The use of isolated human hepatocyte infusions to treat human disease will require safe, acceptable, reliable, and reproducible measures of engraftment and function of the donor liver cell. Cell transplant for inborn errors of hepatic metabolism can be followed by measuring the specific protein missing from the recipient, expressed by the transplanted unmodified donor hepatocytes expressing the genes in question. This chapter will focus on the clinical techniques successful in identifying the engraftment and function of donor human hepatocytes when no specific identifiable genes are expressed by donor hepatocytes in acute and chronic liver diseases treated by cell infusion. Radiolabeling and dye labeling techniques, DNA typing of HLA class I alleles, soluble class I HLA ELISA, real-time quantitative PCR techniques including short tandem repeats analysis will be detailed and critiqued.