Serum protein fractions of patients with Behcet's syndrome (incomplete type, 3 males and 3 females), recurrent aphthous ulcer (4 males and 2 females), simple aphtha (1 male and 2 females) and erythema exsudativum multiforme (EEM) (1 male and 3 females) were analyzed quantitatively by electrophoresis on cellulose acetate membrane and qualitatively by immuno-electrophoresis on agar gel plate' γ-Globulin and α2-globulin were incressed in Behcet's syndrome. γ-Globulin was also increased significantly in recurrent aphthous ulcer and EEM.By immuno-electrophoretic analysis the precipitation lines of haptoglobin (4 in 6 patients), ceruloplasmin (5), transferrin (4), β1c-globulin (3), IgA (6) and IgG (5) were increased in Behcet's syndrome. In recurrent aphthous ulcer the similar tendency was noticed. In EEM ceruloplasmin, haptoglobin, β1c-globulin, IgA and IgG were increased. Increase in these fractions suggests that some immunolgic mechanism may be involved in the etiology of the diseases.