The aetiology of oral lichen lesions is obscure. In this study the frequency of contact allergy to gold in 83 patients with oral lichen lesions was compared with that in two control groups, comprising 319 age- and gender-matched patients with dermatitis selected from files and 83 clinically examined dermatitis patients. All patients were tested epicutaneously with gold sodium thiosulphate. The two control groups tested were under examination for a tentative diagnosis of allergic dermatitis not related to oral problems. The frequency of contact allergy to gold was 28.9% in the patients with oral lichen lesions, 18.2% in patients selected from files, and 22.9% in the clinically examined control patients. The difference in frequency between patients with oral lichen lesions and those taken from files was statistically significant.