Experiments were performed on rats anaesthetized with chloralose. A duodenal segment was perfused with recirculating isotonic saline, and alkalinization of this perfusate (HCO3- secretion) was measured by continuous pH-stat titration. Stereotaxic electric unipolar stimulations were performed in the perifornical region of the hypothalamus. Stimulation points eliciting an increased arterial pressure were stimulated for a period of 15 min. Duodenal HCO3- secretion decreased in 19 out of 25 experiments and increased in four out of 25 experiments. Inhibitory responses to hypothalamic stimulation were blocked either by thoracic epidural anaesthesia or by the adrenolytic agent guanethidine, suggesting a spinal pathway to the duodenum, presumably in the thoracic splanchnic nerves, and involvement of adrenergic neurons.