The last decade has been marked by tremendous advances in the biochemical and functional characterization of TGF-betas and their receptors in normal and transformed cells. TGF-betas have been shown to modulate proliferation, differentiation and motility of different cell types in a number of in vitro model systems and in some cases with some intriguing results. It is obvious that there is no simple pattern that explains the TGF-betas biological activity in vitro and their effects on cell behaviour need to be assessed in the context of an appropriate physiological cellular environment. Cell-cell and cell-matrix interactions, the differentiating status of the cell together with the functional activity of other soluble growth factors can influence how TGF-betas modulate cell behaviour. However, the overwhelming interest in this field shown by clinicians and basic scientists is rapidly increasing our understanding of how growth factors such as TGF-betas regulate the homeostasis of the GI mucosa and their role in gastrointestinal carcinogenesis.