Purpose/Practical Application: Methadone is understudied in rabbits. Plasma concentrations and pharmacodynamics of intravenous (IV) and oral transmucosal (OTM) methadone in New Zealand white rabbits (NZWR) were examined. Protocol: Six healthy, adult NZWR received, in a crossover design (minimum 1-week washout), 1.5 mg/kg IV and 3 mg/kg OTM methadone. Food intake and fecal output were determined for three days prior and three days following treatments. Baseline sedation score, body weight, oral pH, rectal temperature, and respiratory and heart rate (TPR) were obtained. Blood was collected via a dedicated sampling catheter at 0, 2, 5, 10, 15, 30, 45, 60 minutes, and 2, 4, 6, 8, 12, 24, 36, 48 hours. Plasma methadone concentrations were determined using liquid chromatography mass spectrometry. Sedation score and TPR assessments were repeated every 30 minutes for two hours, then every hour for six hours. Individual baseline thermal thresholds were established and re-assessed at 30, 60, 90, 120, 180, 240 minutes post-drug administration. Results are reported as median/range. No adverse effects were noted. Reduction in thermal threshold was noted for 0.5 and 2 hours following OTM and IV administration, respectively. Appetite and fecal production normalized by 12 hours; feces noted at 3[2-6] hours. Sedation was noted at 30 minutes (7[3-9]) and remained elevated up to 3 hours; no sedation with OTM. Physiological parameters were markedly lower with IV, but not with OTM. Thermal threshold (°C) was increased from baseline at 30 (OTM 10.5[5.3-16.9], IV 17.6[10-21]) and 60 minutes (IV 9.7[6.2-13.7]). Remaining data is under analysis.