Levels of zonulin, as advertised, were determined in non-coeliac wheat sensitivity (NCWS) (n = 36), coeliac disease, (n = 37), and ulcerative colitis (n = 20) patients as well as healthy individuals (n = 49). Compared with the cohort of healthy individuals, patient zonulin levels were elevated (all p<0.0001). Levels in ulcerative colitis were higher than those in NCWS (p = 0.004) and coeliac disease (p = 0.005) with no significant differences between NCWS and coeliac disease. Study samples were ran in duplicate. Red horizontal bars represent median levels for each cohort. Differences in levels between study cohorts were evaluated by Mann-Whitney U tests for nonparametric distributions.