Fully expressed Graves' disease involves an accumulation of glycosaminoglycan (GAG) in the retroocular connective tissue which contributes to the pathogenesis of ophthalmopathy. We treated cultured retroocular and dermal fibroblasts with recombinant interferon gamma (100 U/ml) for 16-24h and measured [3H]GAG accumulation. The cytokine stimulated [3H]GAG accumulation in retroocular fibroblast cultures obtained from eight different donors by 36-124% above control values. In contrast, interferon gamma had no consistent effect on macromolecular accumulation in dermal fibroblast cultures derived from the pretibium or from areas ordinarily uninvolved in Graves' dermopathy. These results suggest that retroocular fibroblasts may be uniquely targeted for one action of interferon gamma which involves the modulation of GAG metabolism.