On isolated human adipose tissue of 80 lean und 50 obese subjects of 18 to 72 years of age the mean fat cell diameter and the in vitro release of glycerol and free fatty acids were determined. In obese patients mean and basal re-esterification rate were increased, whereas the norepinephrine-induced stimulation of lipolysis was reduced. The basal lipolysis of normal-weight subjects was independent of age, however, the stimulation of lipolysis induced by 0.1 μgnorepinephrine per ml was negatively correlated to the age of the patients. Basal and stimulated lipolysis was independent of age in obese subjects.