Carfentanil citrate was given orally to five adult brown bears (Ursus arctos) on 14 separate occasions during the winter and summer to determine effective anesthetic dosages and how season may alter these dosages. Lower blood urea nitrogen : creatinine ratios, depressed appetite, and decreased activity levels in the winter versus summer were reflective of different metabolic states, even though bears were not hibernating in the winter. Doses of carfentanil citrate between 6.0 and 15.2 μg/kg were mixed with 5–10 ml of honey, which the bears licked voluntarily from a spoon. During each anesthetization, respiratory and heart rates, hemoglobin saturation, temperature, electrocardiogram, blood gas values, and level of consciousness were monitored and utilized to determine effective dosages. Mean (±SE) dose requirements in the winter were 7.6 ± 0.4 μg/kg, whereas a greater mean dose of 12.7 ± 0.5 μg/kg was required in the summer (P < 0.05). After ingestion began, sternal recumbency occurred in an average of 7.5 min (range: 4–11 min), and full restraint and safe handling was achieved in 21 min (range: 8–40 min). At the end of each procedure, naltrexone was given as the reversal agent at a ratio of 100 mg naltrexone per 1 mg carfentanil, with 25% of the dose given i.v. or i.m. and 75% given s.c. Mean reversal time was 6 min after injection of naltrexone (range: 4–9 min). Rapid induction and recovery times and ease of oral administration make carfentanil citrate an effective anesthetic agent for use in brown bears. However, hypoventilation and respiratory acidosis were noted in all bears, and oxygen insufflation is recommended.