The etiopathology of colonic inertia remains unclear. Current studies show that pancreatic polypeptide-fold family members can serve as regulators of colonic motility and transit. Thus, the cells containing these peptides on colonic mucosa could be abnormal in patients with colonic inertia. We aimed to evaluate the immunocytochemical staining of peptide YY (PYY) and pancreatic polypeptide (PP) immunoreactive cells, and detect if alteration of these cells relates to an increase in enterochromaffin cells (EC) demonstrated by chromogranin A (CgA), in the colonic mucosa of patients with colonic inertia. Nineteen consecutive patients (18 female, 1 male; age, 43.7+/-11.5 years) who underwent subtotal colectomy for colonic inertia were assessed. The control group consisted of 15 patients (all female; age, 50.7+/-12.5 years) who underwent colonoscopic biopsies from the right and left colon for indications other than constipation, inflammatory bowel diseases, diarrhea, or neoplasm. Hollande's-fixed, paraffin-embedded tissues of both right and left colons were collected. Immunocytochemical staining of PYY, PP, or CgA was performed on 4-microm tissue sections with the respective primary rabbit antibody, the biotinylated secondary antibody, and enzyme-labeled streptavidin. The average number of positive cells per microscopic field (200x) was calculated. Positive cells were classified as strongly, moderately, and weakly staining. The proportion of the variously stained cells is expressed as the percentage of the entire positive cell population. On both sides of the colon, the percentages of strongly and moderately stained PYY positive cells were higher in the patient group compared to the controls (right side, 10.6 and 27.3 vs. 6.1 and 18.7%, respectively; left side, 9.4 and 23.9 vs. 6.2 and 23.1%, respectively) (P < 0.01). Furthermore, in the patients with colonic inertia, the percentages of strongly and moderately stained PYY-positive cells were higher in the right-side colon than in the left (P < 0.01). There was no difference in the number of PYY-positive cells between the patients and the controls. PP-positive cells were very rare in all specimens and were found in 7 of 19 cases (36.84%) in the right-side colon and 16 of 19 (84.21%) in the left-side colon in the patient group (P < 0.01, left vs. right). In contrast, the number of EC in the left colon of patients (16.8+/-10.2) was significantly higher than that in the right side (9.4+/-6.0) (P < 0.01) or that in the left side in the control group (10.4+/-6.0) (P < 0.05). We conclude that in the colonic mucosa of patients with colonic inertia, PYY-positive cells present with higher immunoreactivity, indicating that they may contain more hormones, especially on the right side of the colon. However, the PPY- and PP-positive cells did not relate to the increased EC. and It is therefore suggested that the altered PYY in the colonic mucosa may partially contribute to the etiopathology of colonic inertia.