Both metabolic (hyperglycaemia) and haemodynamic perturbations (hypertension) are involved in the pathogenesis of diabetic nephropathy. Mechanical stretch, mimicking glomerular capillary hypertension, plays an important role in diabetic glomerulopathy, which is characterized by excessive TGFβ1 production and extracellular matrix accumulation (Sharma et al., 1996). In diabetes generation of reactive oxygen species (ROS) and compromised antioxidant defenses contribute to the development diabetic complications. Previous studies have shown that mechanical stretch upregulates p38 mitogen-activated protein kinase (p38^MAPK) phosphorylation and increases production of TGFβ1 and fibronectin deposition in mesangial cells (Gruden et al., 2000). We have investigated the effects of mechanical stretch (average 10% elongation, 1 cycle/s, for 2-48 h) on intracellular reduced glutathione (GSH) levels and expression of the antioxidant stress gene heme-oxygenase 1 (HO-1) in human cultured mesangial cells. GSH levels were determined using a spectrophotometric technique, while HO-1 expression was analyzed by western blotting from whole cell lysates using a specific monoclonal antiserum. We further examined whether inhibition of p38^MAPK with SB203580 or inhibition of TGFβ1 signalling with a TGFβ1 neutralizing antibody affects mechanical stretch-induced HO-1 expression. Mechanical stretch upregulated HO-1 protein levels 2-3 fold as early as 3-6 h and this was sustained after 48h (p<0.01 students t-test). In parallel experiments, mechanical stretch for 48h caused a 2-fold increase in GSH levels (15 ± 3 vs 30 ± 3 nmol/mg protein, mean ± S.E.M., n=3, p<0.01). Pretreatment of cells with SB203580 (2μM) or a TGFβ1-neutralising antibody (5μg/ml) caused a further increase in stretch-induced HO-1 expression after 48h. Mechanical stretch is a powerful stimulus for GSH production and HO-1 expression in human mesangial cells. Pathways other than TGFβ1 and p38^MAPK may be involved in the antioxidant response of mesangial cell to mechanical perturbations. Future studies will investigate the role of other MAPK cascades on stretch-mediated antioxidant gene expression and the potential inhibitory role of TGFβ1/ p38^MAPK on stretch-induced HO-1 expression.