Samples of serum from patients with sarcoidosis were examined for the presence of immune complexes, using the Raji cell line. An indirect immunofluorescent technique was used to detect the binding of immune complexes to the complement receptors of Raji cells. Preliminary studies indicated that the method was sensitive and specific. We studied 44 patients with sarcoidosis who were separable into the following three distinct clinical groups: (1) acute disease (one year or less); (2) chronic active disease (five years or more); and (3) resolved disease (five years or more). In the 26 patients with acute disease, 12 had circulating immune complexes; immune complexes were present in two of the ten patients with chronic active disease. In contrast, immune complexes were absent in patients with resolved disease and normal control subjects. In patients with active disease, there was no apparent correlation between the presence of immune complexes and the stage of disease; however, immune complexes were present in five of the 11 patients with extrapulmonary disease, in seven of 12 patients with elevated concentrations of gamma-globulin, and in four of five of those patients with autoantibodies to lymphocytes.