During winter, hibernating animals rely on their lipid stores for survival. In vitro lipolytic activity of isolated adipocytes from gonadal and subcutaneous white adipose tissue (WAT) was studied in captive alpine marmots (Marmota marmota) at two different times of their yearly cycle. During the summer, when marmots were eating, adipocyte responsiveness and sensitivity to isoprenaline and noradrenaline were higher in gonadal than in subcutaneous WAT. During hibernation, when marmots were spontaneously fasting. both the response and sensitivity to catecholamines decreased in gonadal WAT to the level of subcutaneous WAT. A similar pattern of response was also observed when lipolysis was stimulated with glucagon but the lipolytic rate was three times lower than with catecholamines. Adenosine deaminase (ADA) had a marked stimulatory effect on lipolysis, especially during the 'feeding' period, suggesting that adenosine may be a potent lipolytic modulator in marmot adipocytes. It is concluded that in marmots, lipolysis could be differentially regulated between fat depots during the annual cycle possibly to optimize either the building-up or the use of fat reserves.