Abstract:Methoxyflurane and tetracyclines may cause dose‐related renal dysfunction. In the present study rats were treated with oxytetracycline (37.5 and 75 mg/kg/day) or tetracycline (75 mg/kg/day) intraperitoneally for four days and one methoxyflurane anaesthesia (1 % for 45 minutes) was given on the second day. The combined treatment as well as methoxyflurane anaesthesia alone, caused polyuria, elevated urinary fluoride excretion, increased serum uric acid concentration and SGPT activity. The histological examination showed shrinkage of glomeruli and tubular protein deposits in the kidneys and marked fat infiltration in the liver of rats treated with the antibiotics and methoxyflurane, while the anaesthetic seemed to cause only slight fatty changes in the liver. A probable renal tubular lesion caused by methoxyflurane, or its metabolites, was indicated by the polyuric effect, the lack of response to injected vasopressin and the uric acid retention while the tetracyclines probably added to the toxic effect mainly through their anti‐anabolic action. Oxytetracycline, in combination with one halothanc anaesthesia, did not seem to cause hepatotoxicity in the r