The study concerns the histological and immunohistochemical findings of the gastrointestinal mucosa of 20 patients (group A) suffering from contact allergic dermatitis (CAD) to Ni, with symptom recrudescence due to food ingested Ni. Results were compared with those observed in 20 patients suffering from CAD to Ni (group B), without sensitivity to food ingested Ni, and in 20 normal subjects (controls). The sensitivity to food ingested Ni, as suggested by history, was demonstrated by placebo-controlled oral-Ni challenge. The biopsies for histological and immunohistochemical study were performed during endoscopy and obtained from the antrum and from the duodenal mucosa. In the biopsies obtained from 16 of group A patients there was evidence of inflammatory infiltrate of lymphocytes and plasma cells with oedema and vasodilation in the lamina propria. Slight flattening of the villi and enlongation of the crypts were concomitant. These findings were light in the 4 patients of group A and in 11 of group B and instead were absent in the remaining group B patients and in the controls. Immunohistochemically, lymphocytes in the lamina propria were prevalently CD20 + (B cells) and CD4 + (Th cells), some were CD45RO + (memory) and finally few CD8 + (Tc/s cells). CD45RO + cells was found in cluster in patients of group A and in 4 of group B, whereas in the others were isolated. Since some studies have shown that immunological pattern of skin reaction to Ni is characterized by increased CD45RO + cells, it may be hypothesized that in patients suffering from CAD to Ni, the sensitivity to food-ingested Ni may be induced by a type IV immunological reaction in the gut.