Stimulation of the the sympatho-adrenal system and catecholamine production are induced by several factors accompanying shock. The role of hypotension in evoking this response has been thoroughly investigated. Stimulation of epinephrine and norepinephrine in response to shock has been previously documented, both in experimental work and in clinical situations.1The important role of acidosis has been less well elucidated. This report summarizes recent work in this institution, related to the role of acidosis in the stimulation of a sympathoadrenal system, as measured by plasma catecholamine levels. Three experimental models were studied to elucidate clinical observations made during cardiopulmonary bypass. The first series of experiments previously reported by Manger et al2were designed to elucidate the effects of acid-base control on the sympathoadrenal response following irreversible hemorrhagic shock. Shock was produced in mongrel dogs with the preparation described by Wiggers,3with maintenance of mean arterial-blood pressure of 50