Transforming growth factor beta 1 (TGFβ1) downregulates TGFβ receptors and Smad3, and upregulates Smad7. Human articular chondrocytes (HAC) were cultured for 5 to 6 days in 10% FCS-containing DMEM. They were then incubated in DMEM + 2% FCS with increasing doses of transforming growth factor beta 1 (TGFβ1) for 48 hours. TGFβ receptor type I (TβRI), TGFβ receptor type II (TβRII), Smad2, Smad3, Smad4 and Smad7 mRNA were analysed by real-time RT-PCR. The modulation of mRNA expression was expressed relative to the controls (not treated), after normalisation to the GAPDH signal. *, P < 0.05, **, P < 0.01, ***, P < 0.001.