Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) ; ObjectiveTo compare the postoperative analgesic effects of intravenous (IV), intramuscular (IM), subcutaneous (SC) or oral transmucosal (OTM) buprenorphine administered to cats undergoing ovariohysterectomy.Study designRandomized, prospective and blinded clinical trial.Animals100 female cats.MethodsCats were assigned to receive 0.01 mg kg-1 of buprenorphine administered by the IV, IM, SC or OTM route (n = 25/group). Buprenorphine was made up to 0.3 mL with 0.9% saline. DIVAS (0-100 mm) and simple descriptive scale (SDS) (from 0 to 4) pain and sedation scores were assigned to each cat before and 1, 2, 3, 4, 6, 8, 12 and 24 hours after ovariohysterectomy. Buprenorphine and carprofen were administered for rescue analgesia. Data were analyzed using anova and Fisher's exact test (p 0.05). There were no significant differences between groups for sedation scores at any time. SDS pain scores did not detect any differences between groups (p > 0.05). DIVAS pain scores after OTM administration were significantly higher than IV and IM administration at 1 hour and at 3, 4, 6, 8 and 12 hours, respectively (p