The present study was aimed at disclosing the influence of Bacteroides fragilis (one of the most important bacterial agents causing colitis in children) experimental infection on the expression of substance P (SP) and somatostatin (SOM) in neurons and nerve fibres within the porcine ascending colon. Distinct differences in the distribution pattern of neural elements immunoreactive to the substances studied were observed between the experimental (Inflam) and control (Contr) pigs. In general, the number of SP-IR neurons and nerve terminals increased, while the expression of SOM decreased after Bacteroides fragilis-induced colitis (BFIC). However, distinct differences in the intensity of these alterations were observed between particular compartments of the bowel segment studied. Thus, the present results suggest that SP- and SOM-immunoreactive (SOM-IR) elements of the enteric nervous system play a part in the control of colonic activity during BFIC.