Anaesthesia was required in an 18-month-old Dorper ewe scheduled for surgical repair of an abdominal hernia. Anaesthesia was induced with diazepam (0.15 mg/kg) and ketamine (6 mg/kg), and maintained with halothane in oxygen on a circle anaesthetic machine. Hypotension, hypoxaemia, cyanosis and pulmonary oedema were observed from the start of surgery, but the symptoms improved towards the completion of the procedure. The aetiology of this condition could not be established. It is suggested that propylene glycol, the organic solvent in the diazepam formulation, may have stimulated the release of vasoactive substances that resulted in pulmonary oedema.