Vimentin is one of the mammalian intermediate filament proteins. It is expressed in cells of mesenchymal origin and is characteristic of proliferating cells at fetal stage. During malignancy, vimentin expression is activated in certain lung epithelial cells. Examination of a group of lung cancer cells showed marked difference in their vimentin expression. The difference in vimentin expression among lung cancer cells is due to differential regulation at the transcriptional level. Analysis of the vimentin promoter revealed a 102-bp promoter sequence that is important for promoter activity in a lung cancer cell line in which vimentin is strongly expressed. This promoter region interacts with Poly(ADP-ribose) polymerase-1 (PARP-1) which is also a transcription regulator. Exogenous expression of PARP-1 increased vimentin promoter activity. A shortened PARP-1 without the C-terminal catalytic domain showed the same promoter activation effect. Treatment of cells with H₂O₂ resulted in reduced PARP-1 and vimentin expression at the protein level. H₂O₂ also dose-dependently suppressed vimentin promoter activity in cells overexpressing PARP-1. These results demonstrate that vimentin expression in lung cancer cells is regulated at the transcriptional level; and PARP-1 binds and activates the vimentin promoter independent of its catalytic domain and may play a role in H₂O₂-induced inhibition of vimentin expression.