Thirty-seven liver-grafted patients with steroid-resistant acute or chronic graft rejection or with cyclosporin-related complications were converted from CyA to FK 506. The clinical outcome of the patients primarily depended on the degree of liver dysfunction present at initiation of FK 506 treatment. In patients switched to FK 506 for treatment of acute or early chronic graft rejection, CyA nephrotoxicity, or CyA malabsorption, the FK 506 therapy was associated with a clear improvement in the clinical course. In contrast, in patients with advanced chronic graft rejection, a lower response rate to the conversion in immunosuppression was observed. The lower response rate was associated with a higher patient mortality. These studies demonstrate that FK 506 represents a valuable alternative immunosuppressant for liver-grafted patients. The conversion from CyA to FK 506 should take place before serious--and potentially irreversible--disturbances in liver function are observed.