Peyer’s patches (PP) are sites of immune surveillance in the gastrointestinal tract. Nerve fibres underlie the follicular associated epithelium (FAE) in the dome of the PP (Krammer and Kulnel, 1993). The function(s) of such nerves has not been described although the enteric nervous system is known to regulate epithelial ion transport processes in normal and parasitised gut (Stead, 1992). The aim of this study was (1) to quantify the innervation of rat distal colonic lymphoid tissue from rats primed by Fasciola hepatica infection compared to uninfected controls and (2) to examine how electrical field stimulation (EFS) of nerves within PP modifies epithelial ion transport processes in vitro.Adult female Wistar rats were lightly anaesthetised (isofluorane) and orally infected with 20 metacercariae. This study was licensed by the Department of Health and approved by the Institutional Ethics Committee. For immunohistochemical analyses of nerves, five weeks post infection animals were euthanised by overdose of euthatal given by intraperitoneal injection. Post-mortem colonic PP from infected (n=8) and control (n=6) rats were collected, fixed, sectioned and mounted. Nerves were identified immunohistochemically using anti-GAP-43. Image analysis was performed using Image-Pro^® software. In separate experiments, Wistar rats (200-300g) were humanely killed by cervical dislocation and colonic PP epithelium was mounted in Ussing chambers under voltage clamped conditions. The window area (0.28cm2) was completely occupied by Peyer’s patch epithelium. Changes in short-circuit current (SCC) in response to electrical field simulation (EFS; 7v, 7Hz, 1ms, 1 min pulse train) and carbachol (CCh) (10^-5M) in PP epithelium were measured. All data are expressed as mean±s.e.m., comparison between infected and control means were made using unpaired two-tailed student t tests. Immunohistochemical analysis of PP nerves in normal rat colon showed 517±272 nerve fibres per mm² in the dome region (n=6) some adjacent to FAE. Numbers increased significantly with F. hepatica infection (935±87, n=8, P≤0.05). EFS of voltage clamped PP evoked a mean inward SCC of 35±6µA.cm^-2 (n=16) which was accounted for, at least in part, by electrogenic chloride secretion. SCC responses were virtually abolished by tetrodoxin (TTX, 10^-6M). In contrast, ion transport responses to the directly acting secretagogue CCh (10^-5M) were not altered by TTX. These data indicate that the density of PP associated nerves are, as elsewhere in the gastrointestinal tract, raised as a consequence of parasitism. Furthermore, since these nerves regulate chloride secretion, their function may be to amplify protective responses of the parasitised host.