Abstract: The metabolic rate of three captive manatees was measured at different water and air temperatures. The animals responded metabolically to cold water (15-20 C), but not to cold air (10-20 C). Average metabolic rates in the thermal neutral zone (T1=24) were 15-22% of predicted weight-specific values, and thermal conductances were 117-229% of predicted levels. Body temperatures averaged 36.4 C. The low heat production and high thermal conductance suggest that manatees are poorly adapted energetically to winter water temperatures in much of Florida. These results support behavioural observations of captive and free-living manatees which suggest that 20 C is the minimum suitable water temperature for manatees. Manatees wintering in colder waters are probably in marginal habitat and are most susceptible to cold-related mortality. Warm water refuges reduce energetic maintenance costs and probably temper the effects of occasional periods of severely cold weather, particularly in northern Florida.