The partial micro-opioid receptor agonist buprenorphine produces antinociception through mechanisms different from those of classical opioids. In this study, we compared the effect of buprenorphine and morphine on C-fiber conditioning stimulation (CS)-induced facilitation of the flexor reflex, a model of central sensitization in decerebrate, spinalized unanesthetized rats. Intraperitoneal morphine and buprenorphine moderately depressed the baseline flexor reflex to a similar extent at doses of 1-2 and 0.03-0.1 mg/kg, respectively. Buprenorphine significantly reduced C-fiber CS-induced reflex facilitation whereas morphine at 1 or 2 mg/kg had no effect. Thus, some of the atypical antinociceptive effects of buprenorphine may be derived from its effect on central sensitization.