Both acute and chronic liver disease have an effect on renal function. After liver transplantation we have to pay attention to the further loss of function because of applied calcineurin inhibitor treatment. It has nephrotoxic side-effect, so the investigation of renal function is converted into an important mission in liver transplant patients. In our study we compared the results between formulas which use serum creatinine: MDRD, which use albumin, too, has effectively other values than the Cockroft-Gault. We compared the two formulas in a retrospective analysis, in 187 patients at a stated time (before operation, after operation, within 1 week, 1 month). We got higher GFR at each date with Cockroft-Gault; mean differences: 19.56%, 17.33%, 37.18% and 28.8%. In the range of 15-60 ml/min GFR, we found nearly twice as many patients by use of MDRD than by use of Cockroft-Gault. Median with MDRD: 79 ml/min, 65.1 ml/min, 52 ml/min, 49.5 ml/min; median with Cockroft-Gault: 93.8 ml/min, 78 ml/min, 70.1 ml/min, 69.4 ml/min, all are significant ( p < 0.001). Many previous studies have already compared the two formulas in end stage kidney disease. On the basis of these studies, MDRD is suitable also under 30 ml/min GFR, but Cockroft-Gault formula approached real GFR measured with isotope methods only above this value. We got the similar conclusion in the examined patient group. It can be stated that MDRD is more suitable to determine renal function in liver transplant patients.