Brown adipose tissue (BAT) mitochondria are distinct from their counterparts in 
other tissues in that ATP production is not their primary physiologic role. BAT 
mitochondria are equipped with a specialized protein known as uncoupling protein 
1 (UCP1). UCP1 short-circuits the electron transport chain, allowing 
mitochondrial membrane potential to be transduced to heat, making BAT a tissue 
capable of altering energy expenditure and fuel metabolism in mammals without 
increasing physical activity. The recent discovery that adult humans have 
metabolically active BAT has rekindled an interest in this intriguing tissue, 
with the overarching aim of manipulating BAT function to augment energy 
expenditure as a countermeasure for obesity and the metabolic abnormalities it 
incurs. Subsequently, there has been heightened interest in quantifying BAT 
function and more specifically, determining UCP1-mediated thermogenesis in BAT 
specimens - including in those obtained from humans. In this article, BAT 
mitochondrial bioenergetics will be described and compared with more 
conventional mitochondria in other tissues. The biochemical methods typically 
used to quantify BAT mitochondrial function will also be discussed in terms of 
their specificity for assaying UCP1 mediated thermogenesis. Finally, recent data 
concerning BAT UCP1 function in humans will be described and discussed.