It is not clear whether the anaesthetic agents tiletamine and zolazepam have antioxidant or pro-oxidant effects. Therefore, this study was carried out to investigate the effects of tiletamine-zolazepam anaesthesia on oxidant/antioxidant status in blood plasma and on haematological parameters in 10 healthy Awassi ewes. The tiletamine-zolazepam combination was administrated in a dose of 7.5 mg/kg intramuscularly. The animals were spontaneously breathing air during the procedure. Blood samples were collected by jugular venipuncture before induction and at 30, 60, 120 min, 24 h and 3 days after anaesthesia. Malondialdehyde concentration, an index of lipid peroxidation, was higher at 30, 60, 120 min and 24 h (P < 0.05) than the baseline value in the plasma. The level of glutathione decreased (P < 0.05) at 30, 60 and 120 min, then returned to the baseline level. Beta-carotene concentration was lower (P < 0.05) than the baseline value during anaesthesia with the exception of its level at 120 min. Glutathione peroxidase and catalase activities decreased (P < 0.05) at the onset of anaesthesia, then returned to baseline values. There was no significant change in vitamin A level. Red blood cell count, haematocrit and haemoglobin concentration significantly decreased (P < 0.05) only at 30 min and thereafter they gradually returned to the baseline values. Based on the results tiletamine-zolazepam anaesthesia seems to accelerate lipid peroxidation and to impair the enzymatic antioxidant defence in the blood plasma.