Eighty female cats presented for ovariohysterectomy were randomly allocated to one of two treatment groups in this assessor-blinded trial. After pre-anaesthetic assessment, the cats were premedicated with acepromazine (0.1 mg/kg). Anaesthesia was induced with thiopentone and maintained with halothane in oxygen. Forty cats received carprofen (4 mg/kg subcutaneously) and 40 received meloxicam (0.3 mg/kg subcutaneously) after anaesthetic induction. Following routine flank ovariohysterectomy the cats were assessed using visual analogue scale scores for pain and sedation over a 20-hour study period. Blood samples were taken before sedation and at 20 hours for serum biochemistry (urea, creatinine, alanine aminotransferase and aspartate aminotransferase). There were no significant differences between the groups for pain and sedation scores. Serum biochemistry values were similar between the groups, with some differences within groups between the pre-sedation and 20-hour values. One cat in the carprofen group and two cats in the meloxicam group required rescue analgesia with intramuscular morphine (0.2 mg/kg).