Glycogen content was determined both in whole adrenal medullary tissue and in isolated adrenal chromaffin cells, in which it responds to glucose deprivation and restoration. [14C]glucose incorporation into glycogen in isolated adrenal chromaffin cells is increased by previous glucose deprivation ("fasting"). Total glycogen synthase activities are 452 +/- 66 mU/g in whole tissue and 305 +/- 108 mU/g in isolated cells. The Km of glycogen synthase for UDP-glucose is 0.67 mM with 13 mM glucose-6-phosphate and 1 mM without this effector. The in vitro inactivation process of glycogen synthase a has been found to be mainly cyclic AMP-dependent, but it also responds to Ca2+. Total glycogen phosphorylase activities are 8.69 +/- 1.26 U/g in whole tissue and 2.38 +/- 0.30 U/g in isolated cells. The requirements for interconversion in vitro of both glycogen synthase and phosphorylase suggest a system similar to that of other tissues. During incubation of isolated adrenal chromaffin cells with 5 mM-glucose, phosphorylase a activity decreases and synthase a activity increases; these changes are more marked in "fasted" cells. Glycogen content and glycogen synthase and phosphorylase activities are higher in the adrenal medulla than in the brain, suggesting a greater metabolic role of glycogen in the adrenal medulla.