Reactive oxygen species contribute to atherogenesis resulting from endothelial and smooth muscle dysfunction. We have previously reported that oxLDL induces the expression of the antioxidant-like stress protein heme oxygenase-1 (HO-1) in human aortic smooth muscle cells (HASMC, Anwar et al. 2005). HO-1 catabolises the pro-oxidant heme to the antioxidants biliverdin and the vasodilator carbon monoxide (Siow et al. 1999). Transforming growth factor-β1 (TGF-β1) stimulates vascular SMC growth and extracellular matrix synthesis which contributes to vascular remodelling (Topper, 2000). Induction of cytoprotective antioxidant genes such as HO-1 is regulated by the transcription factor Nrf2 and act to limit oxidative injury (Ishii et al. 2000). We have now investigated whether TGF-β1 activates Nrf2 to mediate HO-1 induction and the involvement of mitogen-activated protein kinases (MAPK) and free radical generation in human aortic SMC. Cells were treated with TGF-β1 (0–10 ng/ml, 0–24 h) and HO-1 expression and phosphorylation of extracellular signal-regulated kinase (ERK1/2), p38^MAPK and c-Jun N-terminal kinase (JNK) determined by western blot analyses. Activation of Nrf2 translocation was determined by immunofluorescence and immunoblot analyses of nuclear lysates. NADPH-dependent superoxide generation was assessed by lucigenin chemiluminescence in cell homogenates. The statistical signigficance of quantified data were evaluated using Student’s unpaired t tests. TGF-β1 (2.5 ng/ml, 2 h) treatment led to nuclear translocation of Nrf2, phosphorylation of JNK, p38^MAPK and ERK1/2, and increased superoxide production by 1.5±0.2-fold (mean±SEM, n = 3, p<0.01). Pretreatment of cells with apocynin (100 μM), an NADPH oxidase inhibitor, significantly attenuated superoxide generation elicited by TGF-β1 by 34±8% (p<0.05, n=3). HO-1 expression was enhanced by TGF-β1 (2.5 ng/ml), reaching a maximum 10.3±2.3-fold increase between 8–12 h (mean±SEM, n = 3, p<0.01). Modulation of TGF-β1-mediated Nrf2 activation, free radical production and HO-1 expression may provide mechanistic insights for the contribution of this growth factor to vascular disease processes.