Adrenal medullary cells produce not only the catecholamines norepinephrine and epinephrine but also a number of peptides; hence, they can be subclassified according to their peptide quality. The present study was an attempt to test whether different stressors address different subclasses of adrenal medullary cells. The adrenal gland of intact male rats was implanted with a dialysis system, and the jugular vein was catheterized. One day after surgery, the adrenal dialysis system was connected to a perfusion pump, and Ringer solution was used for dialysis; dialysate fractions were collected at 15-min intervals, and blood was withdrawn at the end of each fraction period after a 2-h equilibration period. The basal release rates of pituitary PRL and adrenal corticosterone, measured in plasma, and of epinephrine, norepinephrine, and substance P (SP) measured in the adrenal dialysates, were constant during the preshock period. SP concentrations in the blood were below the detection limit of the RIA. Application of mild electric foot shock stress resulted in a marked increase in adrenal catecholamine and SP release. Plasma PRL and corticosterone levels also rose during the time of exposure to foot shock, but plasma SP concentrations remained at undetectable values. In contrast, a metabolic stress i.e. insulin-induced hypoglycemia, did not affect adrenal SP release, although adrenal catecholamine release increased to a larger degree than after foot shock stress. Plasma PRL and corticosterone levels also increased during insulin-induced hypoglycemia. It is concluded that an exogenous stressor (electric foot shock) activates adrenomedullary cells containing catecholamines and SP, whereas these cells are not activated by the stress of insulin-induced hypoglycemia.