The participation of sexual hormones in body weight regulation is partly accomplished by altering food intake. Nonetheless, female sexual hormones also alter brown adipose tissue thermogenesis in females. This study was aimed to find out if male hormones could alter brown adipose tissue thermogenesis in male rats. Testosterone was administered by means of Silastic capsules in adult male rats acclimated either at 28 degrees C (thermoneutrality) or at 6 degrees C (cold), treatment lasting 15 days. Food intake and body weight gain were reduced by hormonal treatment. However, brown adipose tissue mass, protein content, mitochondrial mass and GDP-binding were unchanged at both environmental temperatures. Accordingly, testosterone participation in body weight regulation is thought to be carried out without altering brown adipose tissue thermogenesis. A reduction in the weight of the sex accessory glands was also observed after cold acclimation.