Background.An adequate function test for donor livers is still lacking. The monoethylglycinexylidide (MEGX) test, performed in vivo in the donor to measure the metabolic rate of lidocaine conversion to MEGX, has been proposed as a function test for donor livers to predict postoperative organ function.Methods.In the present study, we investigated whether the MEGX formation rate measured in needle biopsy specimens in vitro correlates with the rate of MEGX formation in vivo. The in vivo MEGX test was performed in the donors and in the recipients on days 1 and 2. The in vivo and in vitro MEGX tests were compared with posttransplant liver function in the recipients in order to investigate their possible relevance as predictors of graft function.Results.The MEGX formation rate in needle biopsy specimens in vitro showed a significant correlation with the MEGX serum concentration found in the donor. A low rate of MEGX formation in the biopsy specimens tended to predict initial poor function of the grafts. In the donor, the MEGX test did not correlate with general liver function after transplantation. Only the MEGX serum concentration in the recipients on day 2 gave an indication of graft function.Conclusions.MEGX formation in liver biopsy specimens in vitro properly reflects metabolic function of the particular liver. Therefore, liver biopsies may be a valuable tool to help predict liver function in vivo. However, the MEGX test alone is not sufficient to provide the gold standard to determine liver function in donor and transplantation livers.