We evaluated a standardized colonic air insufflation test in patients investigated for abdominal pain; 195 patients were evaluable. Of 164 patients with functional abdominal pain, 100 of the 128 (78%) with irritable bowel syndrome diagnosed on the basis of two or more Manning criteria (group A) had positive tests, compared with 19 of the 36 (53%) with functional abdominal pain not satisfying the diagnostic criteria for irritable bowel syndrome (group B). Eight of the 10 patients (80%) with structural colonic disease had positive tests (group C), and 3 of the 21 patients (14%) with structural noncolonic causes of abdominal pain (group D) had positive tests (group A vs. B, A vs. D, and C vs. D, p < 0.01). The air insufflation test had a sensitivity of 78% for the diagnosis of colonic pain and a specificity of 61%. The positive predictive value was 83% and the negative predictive value 54%. Sequential tests by two independent observers on 26 consecutive patients showed no inter- observer variation. The colonic air insufflation test warrants further evaluation as an adjunct to the Manning criteria in the diagnosis of irritable bowel syndrome. It can also serve as an investigative tool to define a subset of patients with functional abdominal pain who do not fulfill the current criteria for irritable bowel syndrome yet whose pain actually originates from the colon.