The p16 (MTS1/CDKN2) gene localized at the 9p21 chromosomal region encodes for a cell cycle inhibitor protein and is altered in many human cancers. The frequency of p16 alterations in gliomas exceeds 50%. To restore the missing wild-type p16 gene efficiently in glioma cells an adenovirus vector carrying the full length coding sequence of the wild-type p16 cDNA, Ad5RSV-p16, was constructed. Three human glioma cell lines, U251 MG, U-87 MG and D54 MG, that did not express endogenous p16/CDKN2 gene and were easily infected with adenovirus vectors were selected for these experiments. Introduction of the Ad5RSV-p16 in these malignant glioma cell lines directed the biosynthesis of functional p16 protein in the majority of the exposed cells, significantly inhibited cell growth, influenced cell morphology and modified the transformed phenotype of cells including the ability to form colonies in soft agar. Flow cytometric studies revealed that the majority of the Ad5RSV-p16 infected glioma cells were arrested in the G0-G1 phases of the cell cycle. These results suggest that p16/CDKN2 inactivation is a significant factor in the genesis and progression of gliomas and that the restoration of the wild-type p16 protein could have clinical and therapeutic utility.