This project is a study into the immunopathogenesis of Recurrent Aphthous Stomatitis and Behcet's Syndrome, which will include: measurement of in vitro immune responsiveness of RAS and BS lymphocytes to oral mucosal antigens; determination of tissue specificity of lymphocyte-epithelial cell interactions; investigation of possible bacterial causes of BAS, paritcularly Streptococcus sanguis; and determination as to whether lymphocytes of RAS and BS patients are thymusderived (T) or bone marrow-derived (B). The objectives are: to extend and attempt to confirm previous studies as well as to include Behcet's disease, and to determine whether or not a significant correlation exists between the immunological events observed during each exacerbation and whether or not the degree of reactivity correlates with the severity of the disease.