Vascular endothelial growth factor (VEGF) plays a pivotal role in tumor progression via angiogenesis. Recently, gene transduction of wild-type p16INK4A, tumor suppressor gene, has been shown to result in downregulation of VEGF expression in p16INK4A-deleted glioma cells. Because expression of p16INK4A is regulated by methylation of the p16INK4A gene, we examined whether demethylation of the p16INK4A gene by 5-aza-2'-deoxycytidine (5-azadC) could cause the protein expression of VEGF as well as of p16INK4A in human lung cancer cells. For this, five different lung cancer cell lines with or without loss of p16 activity were used. H841 and Ma-10 cells had the methylated p16INK4A gene without expression of p16INK4A protein, whereas Ma-1 and H209 cells had the unmethylated p16INK4A gene with constitutive expression of p16INK4A protein. Neither the p16INK4A gene nor p16INK4A protein was detected in A549 cells. Treatment with 5-azadC caused demethylation of the p16INK4A gene with reexpression of p16INK4A protein in H841 and Ma-10 (methylated p16INK4A gene dominant) cell, but not in other cell lines such as Ma-1, H209 (unmethylated p16INK4A gene dominant), or A549 (p16INK4A gene deleted). In a parallel experiment, 5-azadC inhibited production of VEGF protein by H841 and Ma-10 cells, especially in the later hypermethylated cells, but not Ma-1, H209, or A549 cells. RT-PCR analysis showed that Ma-10 cells expressed VEGF isoforms 121, 165, and 189, all of which were inhibited by 5-azadC. These findings indicate that the methylation status of the p16INK4A gene plays an important role in the regulation of angiogenesis associated with progression of lung cancer, through regulation of VEGF expression.