Using nanoparticles offers great potentiality and perspectives in novel diagnostic and therapeutic applications. Despite the rapid progress and initial acceptance of nanobiotechnology, adverse effects on human health due to exposure to various concentrations of nanoscale materials have not yet been established. Materials in the nanometer range can exhibit physico-chemical characteristics very different in comparison with particles of same composition but larger size. Properties such as high surface area, high chemical reactivity and the capability to cross cell membranes exploited by research and industry, could also cause adverse effects. As a matter of fact, nanoparticles behaviour in living cells, together with the immunological and metabolic response, is still unclear. In order to identify adverse effects at the cellular level that could give rise to health effects, the evaluation of cytotoxicity of nanoparticles by means of sensitive techniques is an essential approach.