['To study the effects of aldose reductase (AR) on production of fibronectin and type IV collagen in rat mesangial cells (MsC).', 'The vector, pcDNA3-AR, was constructed based on pET-15b-AR. Lipofect AMINE was used for stable transfection and G418 was used for selecting positive clones. Sorbinil and zopolrestat were added for suppressing the activity of AR, respectively. The production of fibronectin and type IV collagen and the activation of Smads and MAPK signal transduction pathway were analysed by western blot and AP-1 activity was analysed by electrophoretic mobility shift assays (EMSA).', 'The normal MsC showed increased expression of fibronectin and type IV collagen with stimulation of TGF-beta1. Compared with the normal MsC, the MsC pre-incubated with ARI showed reduced expression (P < 0.05) and the AR-transfected MsC showed increased expression (P < 0.05). The normal MsC showed activation of ERK, JNK and p38 with stimulation of TGF-beta1, while the activation of JNK and p38 was inhibited in the MsC pre-incubated with ARI and only the activation of JNK was enhanced in the AR-transfected MsC. The normal MsC showed enhanced AP-1 activity with the stimulation of TGF-beta1, and similarly the activity was inhibited in the MsC pre-incubated with ARI and was more enhanced in the AR transfected MsC.'] Does aldose reductase regulate TGF-beta1-induced production of fibronectin and type IV collagen in cultured rat mesangial cells?