['Methane (CH4)-producing intestinal bacteria might be related to constipation. This study was carried out to evaluate the association between breath CH4, colonic transit, and anorectal pressure in constipated patients.', 'A database of consecutive 62 constipated patients fulfilling the Rome III with the lactulose CH4 breath test (LMBT), a colon marker study, and anorectal manometry was studied. The profile of LMBT in patients was compared with 49 healthy controls. The positivity to LMBT (LMBT+) was defined as CH4 of at least 10 ppm in baseline or above baseline within 90 min. There were two types of constipation: normal and delayed transit.', 'There were significant differences in the breath CH4 between patients with delayed transit and (a) normal transit from 0 to 135 min or (b) healthy controls from 0 to 180 min. The LMBT+ was higher in delayed transit patients than in healthy controls (58.8 vs.12.2%) or in normal transit patients (vs. 13.3%), respectively (P<0.01). The delayed transit was the only independent factor for LMBT+ [odds ratio (95% confidence interval), 27.8 (3.32-250.00), P<0.01]. The left and total colonic transit time were significantly increased in LMBT-positive than in LMBT-negative patients. Significant correlations were found between total CH4 and the time of left or total colonic transit. However, no difference was found in the parameters of manometry by LMBT status.'] Is breath methane positivity more common and higher in patients with objectively proven delayed transit constipation?