A qualitative and quantitative determination of serum immunoglobulins was made in 34 patients (27 female, 7 male) with histologically verified oral lichen planus (OLP). The subjects ranged in age from 33 to 80 years and 28 of the cases had OLP changes of atrophic-erosive type. The possible presence of rheumatoid factors (RF), antinuclear antibodies (ANA) or antibodies to mitochondrias, renal glomeruli and smooth muscles was studied in 30 of the patients. The investigation also comprised a control group of 23 patients (17 female, 6 male) without mucosal changes. Immunoelectrophoresis showed an abnormal pattern in 10 OLP cases (29%), the most common change being a polyclonal increase of IgG in 8 persons. Elevated levels of serum IgG (greater than 15 g/l) were seen in a total of 9 OLP patients (26%), but only in 1 of the control cases (4%). The mean IgG value was significantly higher in the OLP than in the control group, 13.4 and 10.3 g/l, respectively. Regarding levels of IgA and IgM, no difference was noted between the groups. Autoantibodies were registered in 27% of the OLP patients and in 9% of the controls. The immune changes could be correlated in some respect to positive fungal cultures, allergies and decreased unstimulated saliva, but not to age, endocrine disorders or joint diseases.