Since the highest plasma epinephrine levels have been recorded during resuscitation, we evaluated the isolated effect of cardiac arrest upon adrenomedullary secretion. We determined plasma epinephrine in dogs resuscitated with cardiopulmonary bypass (CPB) after cardiac arrest periods of 12 (CPB-12; n = 4) or 16 min (CPB-12 and CPB-16 regarding most cardiopulmonary functional variables. Plasma epinephrine was markedly elevated immediately after initiation of CPB (p < .01 at 1 min CPB vs. basal) and returned rapidly to basal concentrations. Comparison of plasma epinephrine levels between CPB and standard CPR groups showed that responses to cardiac arrest were similar (p > .05 at 1 min CPB vs. 11.5 min CPR). We conclude that cardiac arrest is the main or sole determinant of the plasma epinephrine elevation of resuscitation.