Purpose: To identify whether there are preadipocytes in the orbits of thyroid-associated ophthalmopathy (TAO) patients and whether they possess the capacity to undergo adipocytic differentiation. Methods: Orbital fat tissue from TAO patients was placed in primary culture and proliferating cells were sub-passaged. The preadiocytes were identified with immunohistochem-istry. Confluent preadipocytes were subjected to a differentiation protocol. And Peroxi-some proliferators-associated receptorγ(PPARγ) transcript levels were determined before and after differentiation. Result: In primary culture, cells were spindly and showed positive immunostaining for preadipocyte factor-1 (pref-1) protein. During the process of differentiation, orbital cells showed evidence of adipogenesis and relatively greater PPARγgene expression with differentiation. Conclusion: There are active preadipocytes in the orbital tissue of TAO patients which might be able to undergo adipocyte differentiation. These observations suggest t Objective: To identify whether there are preadipocytes in the orbits of thyroid-associated ophthalmopathy (TAO) patients and whether they posse the capacity to under adipocytic differentiation. Methods: Orbital fat tissue from TAO patients was placed in primary culture and proliferating cells were sub- passaged. The preadiocytes were identified with immunohistochem-istry. Confluent preadipocytes were subjected to a differentiation protocol. And Peroxi-some proliferators-associated receptor gamma (PPARγ) transcript levels were determined before and after differentiation. Results: In primary culture, cells were spindly and showed positive immunostaining for preadipocyte factor-1 (pref-1) protein. During the process of differentiation, orbital cells showed evidence of adipogenesis and relatively higher PPARγgene expression with differentiation. Conclusion: There are active preadipocytes in the orbital tissue of TAO patients which might be able to undergo adipocyte differentiation. These obs ervations suggest t