In order to assess the response of plasma biochemical parameters to anaesthesia, 40 New Zealand White (NZW) rabbits were assigned to four treatment groups ( n = 10): control (1 ml i.v. saline solution), fentanyl-droperidol (FD) (0.4 ml/kg s.c. of 'thalamonal' solution; 2.5 mg/ml droperidol, 0.05 mg/ml fentanyl), ketamine (K) (10 mg/kg i.v.) with either xylazine (X) (3 mg/kg i.v.) or diazepam (D) (2 mg/kg i.v.). Blood samples were obtained from the central ear artery at six time points: before injection, and at 10, 30, 60, 120 min and 24 h after injection of the anaesthetics/saline. Plasma ALT, AST, ALP, GGT, BUN, creatinine, phosphate and potassium levels were measured by the Hitachi 747 autoanalyser. The administration of K-X increased ( P < 0.05) plasma ALT (from 11.4 ± 0.9 to 20.2 ± 1.7 IU/l, at 10 min), AST (from 10.5 ± 3.3 to 34 ± 2.1 IU/l, at 120 min), BUN (from 17.2 ± 0.9 to 25.8 ± 1.8 mg/dl, at 60 min) and creatinine concentrations (from 1 ± 0.1 to 1.6 ± 0.2 mg/dl, at 10 min). After K-D administration, we observed an increase ( P < 0.05) in plasma ALT (from 11.4 ± 0.9 to 20.2 ± 1.1 IU/l, at 10 min), AST (from 11.4 ± 1.6 to 28 ± 3.7 IU/l, at 10 min), BUN (from 15.8 ± 0.8 to 30 ± 1.5 mg/dl, at 10 min) and creatinine levels (from 1 ± 0.08 to 2.2 ± 0.2 mg/dl, at 120 min). No significant changes were seen in the FD group. We conclude that K-X and K-D may affect plasma concentration of select serum enzymes and biochemical parameters. These results should be taken into account when blood samples are evaluated in treated rabbits.