Absence of expression of the p16IKN4a gene product is commonly observed in mesothelioma tumors and cell lines, while wild-type pRB expression is maintained. We have examined the biologic and potential therapeutic role of re-expressing p16INK4a gene product in mesothelioma cells and tumors. Following transduction with a p16INK4a expressing adenovirus (Adp16), over-expression of p16INK4a in mesothelioma cells resulted in cell cycle arrest, inhibition of pRB phosphorylation, diminished cell growth, and eventual death of the transduced cells. Expression of p16INK4a protein was accompanied by decreased expression of pRB as detected by immunoblot and immunohistochemistry. Experiments in mesothelioma xenografts demonstrated inhibition of tumor formation, tumor growth arrest and diminished tumor size and spread. p16INK4a gene product expression was also demonstrated in intraperitoneal xenografts of human mesothelioma cells. These results demonstrate that p16INK4a gene transfer may play a therapeutic role in the treatment of mesothelioma.