Using novel in vitro preparations of vascularly perfused rat ileum, we investigated mesenteric afferent sensitivity to vascular perfusion. Gut (GPP) and vascular (VPP) perfusion pressures were recorded simultaneously with afferent discharge (AD). After preconstriction (L-phenylephrine), capsaicin (100 µM, gut lumen) caused a transient increase in AD and a sustained fall in VPP, supporting afferent modulation of vascular tone. In turn, AD was affected by vascular perfusion rate (VPR). Increasing VPR step-wise (0.6 to 1.0, 1.4 and 1.8 ml/min) caused concomitant falls in AD, returning at 0.6 ml/min. Terminating flow (5 min) increased AD. Afferent responses were independent of changes in GPP, vascular O₂, or the gut "tube" ("gut-off"). In gut-off studies, where capsaicin (100 nM ia) still reduced VPP, flow-associated falls in AD were abolished by the enzyme neuraminidase (0.2 U/ml ia or extravascularly over 20 min). In contrast, increased AD after stopped flow was unaffected. We propose that mesenteric afferents "sense" changes in vascular perfusion. The precise stimuli (pressure and/or flow) and the physiological relevance to control of local circulation remain to be determined.