The increased inhaled application of titanium dioxide nanoparticles (TiO(2) NPs) increases the potential pulmonary health risks. The present investigations were carried out to study the TiO(2) NPs-induced apoptosis, oxidative stress and genotoxicity in the human lung cancer cell line, A549, a widely used cell system for pulmonary toxicity studies. Tetrazolium bromide salt and lactate dehydrogenase release assays were used to study the cytotoxicity. The genotoxicity studies were carried out using cytokinesis block micronucleus assay. Apoptosis was confirmed by the formation of apoptotic bodies and altered expression (messenger RNA (mRNA) and protein) of markers such as P(53), P(21), Bax, Bcl(2) and cleaved caspase-3. Cells exposed to TiO(2) NPs (10 and 50 μg/ml) for 6-24 h shows significant induction in oxidative stress, that is, the production of reactive oxygen species and malondialdehyde and decrease in the activity of catalase and glutathione. TiO(2) NPs exposure also induces the formation of apoptotic bodies and micronucleus as marker of genotoxicity. A significant up-regulation in the expression of apoptosis markers such as P(53), P(21) and cleaved caspase-3 was observed, while the levels were down-regulated for Bcl(2) at both mRNA and protein levels. TiO(2) NPs exposure could not pose significant effects on Bax expression. Data indicate that nano-TiO(2) induces oxidative stress, genotoxicity and apoptosis in human lung cancer cell line, A549. Our result also identifies the mechanisms involved in TiO(2) NP-induced changes in A549 cells. Perhaps, reporting for the first time, the association of TiO(2) NPs-induced genotoxicity and apoptosis at transcriptional and translational level in the human lung cancer cell line, A549 cells.