Irritable bowel syndrome, for instance, was recently reported to be largely a manifestation of food intolerance.7 Despite this, and the extravagant claims recently made for food allergy notwithstanding, it is likely that food allergy is an underdiagnosed condition.8 This may, however, be obscured by the exaggerated impression of prevalence gained from studies involving highly selected population samples. Without previous regard to the mechanism involved, we therefore proposed to seek specific food intolerance among patients with unexplained gastrointestinal symptoms.One of the reasons for the scepticism surrounding the subject of food intolerance is the absence of simple and reliable tests for diagnosis. Double blind food challenges are required to establish diagnosis and a number of techniques using this approach are available. In view of the recognition that food induced symptoms may be delayed9 10 and to ensure, therefore, that chronic food intolerance sufferers with late onset of symptoms were not missed, we used food challenges over one week periods, repeated as necessary if more than one food was suspected. The challenges were double blind and placebo controlled.