The mechanisms involved in the increase of orbital retro-ocular adipose tissue that occurs in Graves' ophthalmopathy (GO) are still unclear. In this condition, the orbital tissue shows glycosaminoglycans deposition produced by activated fibroblasts capable of undergoing adipocytic differentiation. Many genes are involved in adipogenic mechanisms including the transcription factor peroxisome proliferator-activated receptor-gamma (PPAR-gamma). We evaluated the level of expression of the PPAR-gamma gene in normal and GO orbital adipose/connective tissue specimens using a quantitative and sensitive reverse transcription (RT) competitive polymerase chain reaction (PCR) assay. Our results show that the expression of PPAR-gamma was significantly greater in adipose/connective tissue from patients in the active stage of GO than in controls (150.8 +/- 103.9 and 24.0 +/- 4.9 amol/micro g of total RNA respectively, p < 0.05), while there was no significant difference between patients with inactive GO (58.8 +/- 40.6 aM/microg total RNA) and controls. These results suggest that increased PPAR-gamma gene expression in the active stage of GO may be dependent on the inflammatory process in this disease. We speculate that the increased orbital fat tissue observed in GO may be a consequence of the anti-inflammatory PPAR-gamma action.