Fourty‐three patients with oral mucosal lesions were divided into 3 groups based on the relationship between lesions and amalgam restorations. Group I consisted of patients with contact lesions confined to mucosal areas in contact with amalgam fillings. Group II patients had lichen planus lesions exceeding the area of contact with an amalgam filling and Group III comprised patients with lichen planus lesions without relation to amalgam fillings. Biopsies were embedded in epon and subjected to autometallography in order to demonstrate a possible accumulation of mercury in the affected mucosa. In 20 our of 21 patients in Group I, 4 of 11 patients in Group II and 4 of 11 patients in Group III, mercury was found in the lysosomes of macrophages and fibroblasts. In Group I the number of celles loaded with mercury was much higher than in Group II and in particular Group III. In the latter groups autometallographically demonstrated mercury was found almost exclusively in macrophages. Nineteen biopsies taken from patients with normal mucosa served as controls. Ten had occlusal (Group IV) and seven buccal fillings (Group V). The biopsies from the latter group were taken from areas opposing amalgam restorations. Two patients had no amalgam fillings (Group VI). The histochemical technique showed that three biopsies in Group IV (occlusal fillings only) and two in Group V (opposing buccal fillings) contained traces of mercury in the juxtaepithelial connective tissue. The silver enhanced mercury was found in macrophages. The two controls (Group VI) without amalgam fillings were devoid of precipitates. Thus, the present study documents for the first time 1) that mercury is taken up by the lesioned oral mucosal membrane, 2) that under certain, at present unknown, conditions mercury can also penetrate the intact oral mucosa without causing clinical or histopathologic change