OBJECTIVE Disturbances in amino acids metabolism are common in chronic renal failure and subside partially after renal tranplantation. Tryptophan (TRP) is one of the most important exogenous amino acids. Its main derivative is L-kynurenine (KYN). Disorders in the TRP metabolism via kynurenine pathway may lead to neurologic disturbances, hypertension and anaemia. The aim of this study was to assess peripheral kynurenine pathway in 28 renal allograft recipients (RAR) (12 women and 16 men) in comparison to 10 hemodialysed patients with chronic renal failure (CRF) and 10 healthy subjects. METHODS TRP, KYN, 3-hydroxykynurenine (3-HKYN), kyn-urenic acid (KYNA) and quinolinic acid (QA) were determined in plasma using high performance liquid chromatography technique. RESULTS The plasma concentration of tryptophan in RAR was not significantly different from the control group, but it was almost twice higher than in CRF. There was an increase in most of kynurenine metabolites in RAR as compared to healthy subjects, although not as high as in CRF. We found a significant negative correlation between TRP and serum concentration of urea and creatinine as well as a positive correlation with GFR. CONCLUSIONS Kidney transplantation tends to normalize TRP level and markedly lowers blood concentration of kynurenine and its main derivatives. A significant negative correlation was found between TRP level and the concentration of urea and creatinine. Lowering of the KYN metabolites level may play a role in lessening uremic neurological symptomes as well as hypertension and anemia in kidney graft recipients.