Sympathoadrenergic inhibition of HCO3- secretion by the duodenal mucosa was studied in chloralose anesthetized rats. Duodenal HCO3- secretion was measured in situ by pH-stat titration. Direct efferent electrical stimulation of the cut splanchnic nerves (10 Hz, supramaximal intensity) inhibited the duodenal alkaline output by approximately 50%. This inhibitory response was blocked by the administration of either the adrenolytic agent guanethidine or the alpha 2-adrenoceptor antagonist yohimbine. However, neither the alpha 1-adrenoceptor antagonist prazosin nor the beta-adrenoceptor antagonist propranolol blocked the response to splanchnic nerve stimulation. The present data suggest that electrical splanchnic nerve stimulation inhibits duodenal HCO3- secretion via activation of adrenergic nerve fibers and alpha 2-adrenoceptors within the peripheral nervous system.