Measurement of serum immunoglobulin levels in 45 healthy Negro subjects and 52 healthy white subjects revealed significantly higher IgG and IgA levels in the Negroes. Serum immunoglobulin levels were determined in 73 Negro and 12 white patients with sarcoidosis. Levels of IgG and IgA were within normal range in all 12 white patients; IgM levels were increased in 3 patients. Among Negro patients with sarcoidosis, elevation of the IgG value was also infrequent, with mean levels significantly increased only in patients with chronic and stage 3 disease. Levels of IgA were significantly elevated in all types and stages of sarcoidosis, most markedly in those patients with chronic and advanced disease. Levels of IgM were frequently elevated, showing little relationship to stage or duration of disease. Two patients with sarcoidosis had no measurable IgA in their serum.