Nano-sized titanium dioxide (TiO₂) is one of the widely produced and utilized engineered metal oxide nanomaterials. The enhanced utility of these nanoparticles compared to other metal oxide nanoparticles can be attributed to their extraordinary electronic, optical, magnetic and catalytic properties compared to their corresponding bulk forms. Wide-spread application of these nanomaterials in various sectors, namely, food, cosmetics, electronics, construction and in biomedicine has enhanced their production in recent years. Currently, the annual production of TiO₂ exceeds four million tons per year. Use of these materials in consumer products and reports on their entry into ambient atmospheres is a cause for health concerns. Yet, information on toxicity of these nanomaterials is not very clear. In this work, well-characterized TiO₂ nanoforms (e.g. different sizes, crystallinity and surface modifications) were screened for in vitro cytotoxicity in two cell lines (J774 & A549). Cells were exposed to (0-100 µg/cm²) these nanoparticles and various cytotoxicity endpoints (LDH release, ATP, CTB) were analysed, 24 h post exposure. Bulk TiO₂ was used as a reference in these exposure experiments. Cellular oxidative stress levels were determined (GSH/GSSG).  Also, secreted proteins were tested after exposure of cells to these TiO₂ nanoforms using multiplexed affinity-based protein array analysis. NP form-, exposure dose-, cell type-specific cytotoxic responses were observed, with relative potencies of NPs being influenced by physicochemical properties (e.g. metal content, zeta potential, size). Oxidative stress and inflammatory mechanisms appeared to contribute to NP cytotoxicity characteristics. These findings support risk analysis on these nanoforms and also inform on selection of safer materials for technological applications.