118 patients with oral lichenoid lesions (OLL) topographically related to dental fillings were patch tested (PT) to reveal contact allergy to restorative materials. 80 (67.8%) patients displayed positive PT reactions to metals of dental filling materials: 76 reactions were found to various mercury compounds, 4 to sodium aurothiosulphate, 3 to stannic chloride and 2 to silver nitrate. The positive patch test reactions appeared more commonly in patients with restricted contact lesions (85.1%, type-1 lesions) as compared to patients with lesions exceeding to the adjacent areas (38.6%, type-2 lesions). The replacement of dental fillings was carried out in 62/80 PT-positive and 15/38 PT-negative patients. 28 out of 62 (45.2%) PT-positive and 3/15 (20%) PT-negative patients showed complete healing of OLL after a mean follow-up time of 16 months. Complete healing occurred in 29/54 (54.0%) type-1 and 2/23 (8.7%) type-2 lesions. Topographical relation between the lesion and the filling material (restricted versus exceeding the contact area) indicated association of OLL lesion and the filling material, which could be further confirmed by patch testing in the majority of patients. The patch test series should include mercuric chloride (0.1%), mercury (0.5%) and mercury ammonium chloride (1.0%), each in pet.