Tacrolimus has been found to be useful in clinical solid organ transplantation. A very careful monitoring of the tacrolimus levels and dose adjustments are essential, at least in the immediate post-liver transplantation, situation. However, quite often after liver transplantation, patients have limited venous access for daily monitoring of tacrolimus levels. When the blood is sampled from a multilumen central venous catheter, used also for intravenous administration of tacrolimus, falsely elevated concentrations of tacrolimus have been observed. The present study examines the concentration of tacrolimus in capillary blood samples obtained from finger stick and compares its concentrations in simultaneously drawn samples from arterial line, peripheral venous puncture, and multilumen centrally placed venous catheter from the port used for tacrolimus infusion and the port not used for tacrolimus infusion. Ten adult post-liver transplantation recipients were studied. Whole blood concentration of tacrolimus in capillary blood was comparable to that of arterial blood, as well as to that of peripheral venous blood samples (r2 = 0.99; P = 0.72). Concentrations of tacrolimus in venous blood drawn from the port of the multilumen catheter used for intravenous tacrolimus infusion were 3-23 times higher (P = 0.0015), while the concentrations of venous blood drawn from the port not used for tacrolimus infusion were 1.7-4.5 times higher (P = 0.016), as compared with arterial, capillary, or peripheral venous whole blood concentrations.