In order to evaluate the effect of cyclosporine (CsA) versus FK506 on glucose and lipid metabolism, an oral glucose tolerance test (OGTT) was performed in 101 patients after orthotopic liver transplantation (OLT) (mean interval after OLT: 511 days). The liver graft recipients had been randomized prospectively to two groups prior to OLT to receive either immunosuppression with CsA, azathioprine, and corticosteroids (CsA group) or FK506 and corticosteroids (FK group). Along with the OGTT, serum insulin, insulin C-peptide and glucagon as well as serum lipids were monitored. There was no statistically significant difference in the occurrence of impaired glucose tolerance (IGT) or manifest diabetes mellitus disease between the two groups. In fact, not a single patient developed new-onset diabetes in any group. In male and female patients, serum levels of cholesterol and triglycerides increased significantly under FK506 and CsA treatment after OLT. Cholesterol was significantly higher in the CsA group in men, in women this was marked, but not significant. While triglycerides were significantly higher in women on CsA treatment, there was no such difference in men. In conclusion, both CsA and FK506 proved to have similar effects on glucose metabolism, while there was a different spectrum of serum lipid alterations.