"In vitro" studies, carried out on cell cultures, reducing the use of animal research, play a key role in the evaluation of the cytotoxicity of substances of different origin. Cell viability and proliferation are the most investigated endpoints, and different in vitro methodologies, based on colorimetric or fluorescent dyes as markers of cell viability on the basis of cellular metabolism and membrane integrity, are employed . In order to evaluate the cytotoxicity of nanoparticles, the IREA researchers are involved in developing different methodologies aimed to increase the reliability of results. In particular, fluorimetric and flow-cytometric assays, and confocal microscopy procedures are developed in healthy and cancer cell cultures. Employing healthy and cancer cells will allows to detect differences in the response which can be exploited for diagnostic and therapeutic purposes.