Here for the first time we showed, despite the oncogenic mutations in beta-Catenin, that TGF-beta is a modulator of beta-Catenin levels in tumoral fibroblasts as well as non-tumoral fibroblasts. The results show that the TGF-beta pathway is active in desmoids cells and in in situ tumors. A dose dependent increase in beta-Catenin protein levels was observed after TGF-beta treatment in combination with an increased repression of GSK-3beta both in normal and tumoral fibroblasts. TGF-beta stimulation also led to an altered -- up to 5 fold -- transcriptional activity of beta-Catenin responsive promoters, such as IGFBP6 as well as increase of TOPflash activity. TGF-beta stimulation increased cell proliferation and BrdU incorporation 2.5 times. Taken together, we propose that TGF-beta is a modulator of beta-Catenin levels in tumoral fibroblasts and non-tumoral fibroblasts, despite the oncogenic mutations already present in this gene in tumoral fibroblasts of desmoid tumors. This modulation of beta-Catenin levels by TGF-beta may be involved in determining the tumoral phenotype of the cells.