It has been shown that there is a Substance P (SP) containing neuronal projection from the dorsomedial hypothalamus (DMH) to the paraventricular nucleus (PVN)(Bittencourt et al.,1991), evidence presently suggests that this pathway may be important for integration of the stress response. Previously, however, there have been no electrophysiological studies on the DMH to PVN connection. To characterise this connection, electrophysiologically, we used cell-attached patch-clamp recording; we measured action current frequency in the PVN upon stimulation of the DMH with glutamate in rat hypothalamic sagittal brain slices. Glutamate (5mM) application to the DMH increased action-current frequency in the PVN in 9/17 neurones by 519±61% (n=9) p<0.005. Increases in action current frequency in the PVN mediated by glutamate application to the DMH was prevented by the glutamate antagonist kynurenic 200µM acid p<0.005 (n=7) or synaptic block with a high Mg²⁺/low Ca²⁺ buffer solution p>0.05 (n=6). Crucially, the selective NK1 antagonist L-703606 (1µM) also inhibited DMH to PVN neurotransmission p<0.0005 (n=5). This work therefore shows for the first time, an excitatory connection between the DMH and PVN utilising tachykinin NK1 receptors. This pathway may be important for the hypothalamic control of neuroendocrine and/or cardiovascular function.