In fourteen patients with food allergy, intragastral provocation under endoscopical control (IPEC) was performed. In all patients positive immediate-type reactions of the gastric mucosa were observed consisting of oedema, erythema and petechial bleeding. Microscopically, mast cell degranulation was observed and measured by mast cell counts using the o-phthaldialdehyde technique. Concomitantly, tissue histamine content in gastric mucosa decreased significantly after allergen provocation, while there was no change in normal volunteers. Plasma histamine concentration increased in most patients; the increases were most evident in four patients showing mild systemic reactions (urticaria and bronchospasm). The technique described might prove to be useful in establishing the diagnosis in doubtful cases of food allergy.