No differences were observed in heat production or body core temperature between birds provided or not and 400 ppm ascorbic acid. This suggests that ascorbic acid has no effect on heat loss. Birds provided ascorbic acid did exhibit a significantly lower respiratory exchange ratio suggesting a greater utilization of lipid for energy production. Although lipid has a lower heat increment compared with protein and carbohydrate, the significance of this finding to birds exposed to elevated temperature is not known.In conclusion, under the conditions of this study the provision of supplemental ascorbic acid to broiler chickens maintained at an elevated temperature did not affect heat loss as inferred from measured heat production and body core temperature.