We subsequently examined gene expression and methylation patterns for the IGF II gene in both control tumors and tumors treated for 1 week with budesonide. Expression levels of the IGF II gene were increased roughly 2.5-fold in tumors vs normal lung parenchyma. This overexpression was reversed by treatment with budesonide for a period of 7 days. We also examined the methylation at CpG sites within the DMR2 region, which includes exons 4, 5, and 6. Within the examined region of roughly 600 nucleotides, there were 27 CpG sites. The determination of methylation in this region employed DNA isolation and bisulfite treatment, followed by amplification, cloning, and subsequent sequencing. The percentage of methylated CpG sites was 70% for normal lung parenchyma, 5% for control lung tumors, and 16% and 46% for lung tumors treated with budesonide (0.6 or 2.4 ppm, respectively, in diet) for 1 week. Thus, a chemopreventive agent, budesonide, could rapidly reverse both the generalized and specific hypomethylation observed in mouse lung tumors.