We studied the effects of a 3-day fast and 20 days of refeeding on lipoprotein lipase activity (LPL) in the interscapular brown adipose tissue (BAT) of sexually mature male rats. Rats were refed either ad libitum or restricted quantities (75 or 50% of normal ad libitum food intake). BAT-LPL, expressed on a per depot basis, decreased with fasting and returned to control values by day 3 of refeeding ad libitum. In contrast, refeeding restricted quantities for 5 to 20 days limited regain of body weight and increased BAT-LPL significantly above the values observed in rats refed ad libitum. These adaptations in BAT-LPL activity differ markedly from those observed in rat white adipose tissue or heart muscle and may serve to increase the supply of fatty acids from circulating lipoproteins for BAT metabolic needs and maintenance of thermogenesis during undernutrition.