Sera of 32 patients with sarcoidosis or the benign hilar adenopathy syndrome have been studied by Ouchterlony double diffusion in agar. Antigens have consisted of defatted tuberculin-like material derived from type strains of anonymous mycobacteria. Sera were obtained from several distinct geographic areas of the United States. Twenty-seven of 32 patients produced at least 2 bands against scotochromogenic antigens. Additional reactions against photochromogenic and non-chromogenic antigens were found in a number of sera, but these reactions had a geographic variation corresponding to reported frequency of these organisms. Reactions against antigens of fungi and of H37Rv have been quite rare. Controls, consisting of allergy patients, patients with tuberculosis and of medical students, have shown either no reactions or entirely different patterns. The discovery of these antibodies may furnish an additional diagnostic tool for sarcoidosis and may eventually afford clues as to etiology.