Therapeutic drug monitoring is critical to avoid overimmunosuppression or underimmunosuppression in young pediatric transplant recipients. The objective of this study was to examine cyclosporine (CsA) trough (C0) and 2-hour post-dose (C2) concentrations in the early period after liver transplantation (OLT) to determine whether CsA C2 monitoring is justified. Seventeen infants younger than 2 years treated with CsA (Neoral) were monitored at C0. The biopsy-proved acute rejection rate was 65% at 3 months post-OLT. No correlation was observed between values at C0 and C2. Poor absorption of CsA was observed in most infants during the first 2 weeks post-OLT, as well as interindividual variability in CsA clearance. Exposure to CsA could not be estimated using either C0 or C2 determinations in the early post-OLT period. As a marker of poor absorption, C2 is useful but does not indicate delayed or rapid clearance of drug without simultaneous measurement of concentration at C0. We suggest the use of both C0 and C2 monitoring, or AUC monitoring on an individual basis during at least the first 2 weeks post-OLT.