In rats anaesthetised with urethane, electrical stimulation of the thoracic cord at T 9–10 evoked antidromic responses in neurons in the parvocellular portion of the ipsilateral paraventricular nucleus. Estimated conduction velocities in the spinally-projecting axons ranged from 0.6–5.9 m/sec. The majority (97%) of spinally projecting neurones were quiescent. Increases or decreases in the level of baroreceptor stimulation produced by intravenous injection of phenylephrine (1–5 μg) or sodium nitroprusside (10–15 μg) inhibited and excited amino acid-induced activity in5/8 and4/11 neurones respectively. Stimulation of vagal afferent endings by rapid bolus injection of 5-HT, to evoke the Bezold-Jarisch reflex, inhibited amino acid-induced activity in15/18 cells. Activation of gastric vagal afferents by distension of the stomach had no effect on paraventriculo-spinal cells. It is suggested that at rest the excitability of paraventriculo-spinal neurons is depressed by a tonic inhibitory input which arises from vagal afferent fibres in the heart.