In order to evaluate the role of glucagon in brown adipose tissue (BAT) function under cold or stress, the changes in immunoreactive glucagon of BAT and plasma as well as uptake and metabolism of radioactive glucagon (125I-G) in this tissue were studied in rats. Glucagon per g fresh tissue was higher in the dorso-cervical BAT than in the interscapular BAT. In warm controls (WC), acute cold exposure (-5 degrees C, 15 min) (CE) or stress (immobilization, 30 min) (AS) elevated glucagon of both sites of BAT as well as plasma. In cold-acclimated animals (CA), the resting levels of BAT glucagon, but not plasma glucagon, were higher than WC. CE caused elevation of plasma glucagon, but not BAT glucagon in CA. AS did not affect glucagon levels in both plasma and BAT in CA. Cold acclimation did not influence 125I-G uptake by BAT, but resulted in a rather lower 125I-G level in plasma and liver. The present results suggest that BAT is a target tissue for glucagon to cause nonshivering thermogenesis in response to cold or stress and that turnover of glucagon is enhanced by cold acclimation.