Cyclosporine A (CsA) bioavailability after i.v. and oral administration was studied in six stable liver transplant patients with open and clamped bile drain. CsA levels were determined by the high-performance liquid chromatography method (HPLC). External bile drainage decreased CsA absorption considerably. Clamping the bile drain resulted in higher and earlier peak CsA levels. Clamping the bile drain increased the bioavailability (9.6% vs. 7%, p < 0.05), but even then it was considerably lower than the value of approximately 30% generally reported in literature. It is recommended to continue i.v. CsA administration to obtain therapeutic plasma concentrations. Early bile drain clamping or bile refeeding will improve CsA absorption and may also result in continuously therapeutic CsA levels.