As part of studies on the pathogenesis of exophthalmos of Graves' disease, the biochemical composition of human retrobulbar tissue was intestigated. The connective tissue was composed of 72.7% lipid, 23.8% water and 3.5% dried defatted tissue. Total tissue glycosaminoglycan (GAG) amounted to 0.18% of dried defatted tissue. Approximately 27% of the total hexosamine and 19% of the total tissue galactosamine were recovered in the GAG fraction. Cellulose microcolumn fractionation of GAG showed that the hyaluronic acid and dermatan sulfate were the two major GAG species.